# Thermostat Caught Fire



## Dennis Alwon (May 9, 2009)

I got a call last night from a customer because her kids room was full of smoke. The firemen told her to call the electrician. I couldn't go so I got my friend- another EC to go check it out. Apparently the thermostat had 45 volts on it somehow and it melted the entire T-stat. Never seen this before. How does 45 V get into those thermostat wires. The T stat wires were not shorting to any line voltage wires.

To see the picture better hit ctrl + to enlarge or ctrl - to decrease.


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## McClary’s Electrical (Feb 21, 2009)

Dennis Alwon said:


> I got a call last night from a customer because her kids room was full of smoke. The firemen told her to call the electrician. I couldn't go so I got my friend- another EC to go check it out. Apparently the thermostat had 45 volts on it somehow and it melted the entire T-stat. Never seen this before. How does 45 V get into those thermostat wires. The T stat wires were not shorting to any line voltage wires.
> 
> To see the picture better hit ctrl + to enlarge or ctrl - to decrease.


 
The control transformer in the unit had an intenal short that changed it's turn ratio. Glad it didn't burn the house down


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## Dennis Alwon (May 9, 2009)

Shouldn't there be a control of some sort to prevent this?


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## McClary’s Electrical (Feb 21, 2009)

Dennis Alwon said:


> Shouldn't there be a control of some sort to prevent this?


 

Good idea, but that's something that very seldom happens. It would take some solid state circuitry to monitor and control that. As you can see, the fuse doesn't mind the voltage as long as the amperage is ok. Cool pics. Thanks for posting


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## HARRY304E (Sep 15, 2010)

Dennis Alwon said:


> Shouldn't there be a control of some sort to prevent this?


 Thats a great queston...I wonder if some type of in line fuses would have helped?


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## HARRY304E (Sep 15, 2010)

Dennis Alwon said:


> Shouldn't there be a control of some sort to prevent this?


How about all the other low voltage transformer's out there?
there is a lott of low voltage lighting out there the same thing could happen in those units as well.


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## macmikeman (Jan 23, 2007)

Wall warts are ugly but they usually have a built in one time fuse to protect against short circuit in either the primary coil or secondary side. At least the wall warts are protected.


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## Dennis Alwon (May 9, 2009)

HARRY304E said:


> Thats a great queston...I wonder if some type of in line fuses would have helped?


The problem is a fuse works on amps not voltage. Unless the load changed the fuse would probably do nothing. I am not sure how you could accomplish a interruption if the voltage changed.


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## mattsilkwood (Sep 21, 2008)

Dennis Alwon said:


> The problem is a fuse works on amps not voltage. Unless the load changed the fuse would probably do nothing. I am not sure how you could accomplish a interruption if the voltage changed.


 You could install a fuse that just barely covers the load, If the voltage goes up so does the amp draw.


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## nrp3 (Jan 24, 2009)

Thats a first.


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## Wirenuting (Sep 12, 2010)

I've seen this a few times on older control transformers. Newer ones that are internal to a unit normally are protected. Need to check the furnace and see if it's an old unit or if a repair had been made with an unprotected transformer. 
Some times people tie an add on humidifier to it and sooner or later she goes poof. But normally it just opens. 

Those folks were lucky.

When I was a kid I smelled smoke all day. In the evening we heard a popping in the basement. The transformer for the door bell caught fire and started burning the joist it was nailed to. 
Since then every open transformer I install on a joist has a sheet metal shield behind it. 50 cents goes a long way.


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## Dennis Alwon (May 9, 2009)

Wirenuting said:


> I've seen this a few times on older control transformers.


This unit is less than 5 years old. Why a t-stat is in a child's bedroom is beyond me. The wire was exposed in the closet so it as adding on after the fact.


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## macmikeman (Jan 23, 2007)

The plus side to this is now the kids interest in electricity and its awesome powers is probably upgraded. Maybe a future electrician or fire(gender bolded here for the political correct ) *man. *


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## Wirenuting (Sep 12, 2010)

Dennis Alwon said:


> This unit is less than 5 years old. Why a t-stat is in a child's bedroom is beyond me. The wire was exposed in the closet so it as adding on after the fact.


I'm surprised the stat is in the bedroom. Was it baseboard? 
Being so new makes me think it's a recall issue. Most furnace manufactures don't recall things. They do the same as car dealers. The TSB route. If you complain about something it's a free warrantee repair. 
Just like my Toyota power sliding doors that broke. No recall, just a technical service bulletin.


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## Dennis Alwon (May 9, 2009)

Wirenuting said:


> I'm surprised the stat is in the bedroom. Was it baseboard?
> Being so new makes me think it's a recall issue. Most furnace manufactures don't recall things. They do the same as car dealers. The TSB route. If you complain about something it's a free warrantee repair.
> Just like my Toyota power sliding doors that broke. No recall, just a technical service bulletin.


It's a central unit. I wasn't there but my friend said it was an odd place. Perhaps the only space with a closet to bring the wires down. They didn't fish them for some reason.


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## Wirenuting (Sep 12, 2010)

Dennis Alwon said:


> It's a central unit. I wasn't there but my friend said it was an odd place. Perhaps the only space with a closet to bring the wires down. They didn't fish them for some reason.


People do strange things when in a hurry. 

Now I have seen a few digital stats for building automation smoke. But that was because of pennies being used to short the sensing element. 
More heat.


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## 76nemo (Aug 13, 2008)

That could of easily been avoided by a thermistor or PTC. Problem is that they're not required to have that protection to be listed.


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## Big John (May 23, 2010)

I would have like to have seen the transformer.

A fuse may have prevented this, but it's supposed to be a Class 2 system, and the whole idea behind Class 2 is that it's inherently protected so it doesn't need fuses. The transformer is supposed to be designed so that if it does fail, it fails in a safe manner. 

I know not everything works as planned, but something here seems out of whack.

-John


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## erics37 (May 7, 2009)

I see a pretty decent amount of burnt up thermostats. None that actually got to the point of catching fire like yours did, but still plenty of damage and melting and stuff.

Recently went out on a service call... some guy had a digital programmable stat that smelled "funny" .... turns out it was starting to melt down. The guy had about 23 amps worth of heaters running off this stat, which was only rated for 19 amps. So it took a few years, but eventually it melted down.

Can't say I've seen a low voltage stat burn up yet, though... all the ones I've seen are digital line voltage stats.


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## sparks134 (Jan 30, 2009)

macmikeman said:


> The plus side to this is now the kids interest in electricity and its awesome powers is probably upgraded. Maybe a future electrician or fire(gender bolded here for the political correct ) man.


That's one of the reasons I became a sparky, when I was a little tike I slide a penny down the wall and it hit the hot and neutral... Puff... Sparks and smoke. Good thing the fuse popped and no fires. It looked really cool though!


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## danickstr (Mar 21, 2010)

sparks134 said:


> That's one of the reasons I became a sparky, when I was a little tike I slide a penny down the wall and it hit the hot and neutral... Puff... Sparks and smoke. Good thing the fuse popped and no fires. It looked really cool though!


Just bare open hots and neutrals around children? Where were you?


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## frenchelectrican (Mar 15, 2007)

By judging the burn / smoke pattern that is pretty odd place to start the burn there.

It will be nice to see the transfomer and the conductors if there were any predamage there.

Merci.
Marc


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## McClary’s Electrical (Feb 21, 2009)

danickstr said:


> Just bare open hots and neutrals around children? Where were you?


 
I think he hit the prongs of a cord end


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## sparks134 (Jan 30, 2009)

danickstr said:


> Just bare open hots and neutrals around children? Where were you?


I forgot to tell you it slide between the outlet and lamp plug...


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## sparks134 (Jan 30, 2009)

mcclary's electrical said:


> I think he hit the prongs of a cord end


Yes... Thank u


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## Dennis Alwon (May 9, 2009)

The only damage visible is at the T-stat. The T-stat wires are fine except where they connected at the stat. The trany is in the attic in the furnace and looks unscathed. 

It seems clear there was a spike that got the t-stat going. I am quite surprised that 46V would do it but perhaps it was higher at one point. This is a day after the smoke damage.


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## Jlarson (Jun 28, 2009)

Oh wow that one really went up. I've seen similar stuff but usually the stat just lets out magic smoke and the fault in the stat clears its self, I've never seen one start on fire.


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## nrp3 (Jan 24, 2009)

I may have missed it, but was it a programmable or a honeywell round?


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## Optohmus Prime (Jan 4, 2011)

Dennis - just for curiosity, was there mercury in this stat? if so, what happened to it?


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## McClary’s Electrical (Feb 21, 2009)

Optohmus Prime said:


> Dennis - just for curiosity, was there mercury in this stat? if so, what happened to it?


 

Not trying to answer for Dennis, but 'd bet next weeks pay that it was solid state. I don't think 48 volts would hurt mercury.


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## Optohmus Prime (Jan 4, 2011)

agreed, but what about the heat affecting the glass bubble?


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## Dennis Alwon (May 9, 2009)

Optohmus Prime said:


> Dennis - just for curiosity, was there mercury in this stat? if so, what happened to it?


I doubt it but who knows it is gone. Here is another horrible picture of the T-stat wires and what is left of the T-stat.


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## McClary’s Electrical (Feb 21, 2009)

Optohmus Prime said:


> agreed, but what about the heat affecting the glass bubble?


 

VERY intersting question. What's the boiling point of mercury? How much pressure could the little vile hold?


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## Charlie K (Aug 14, 2008)

Most low voltage thermostats have a heat anticipator. It is usually a piece of nichrome wire or a coil of very fine wire. The purpose of it is to prevent the room from getting too warm before the thermostat responds. 
if the relay or gas valve was to short this anticipator can get very hot very fast. If it was dusty or dirty it could ignite. The round stat T87 and the old rectangular T82 stats hace this anticipator.

Charlie


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## Dennis Alwon (May 9, 2009)

nrp3 said:


> I may have missed it, but was it a programmable or a honeywell round?


From the remains and what I know of the area it is rectangular. Rarely do we see the round unless it is just heat. 

The t-stat was moved from the hall, that was open to the first floor, to the kids room because they had trouble keeping it comfortable.


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## Charlie K (Aug 14, 2008)

Dennis, a few questions. Who determined 48 volts on the stat?
How did they determine it? Is this a heat/cool system or heat only? And last but not least what all had to replaced to get the furnace running.

Charlie


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## Dennis Alwon (May 9, 2009)

Charlie K said:


> Dennis, a few questions. Who determined 48 volts on the stat?


I was not there but my ex employee who has his own company went there for me as I could not go.



> How did they determine it?


He used an ideal multimeter- I think. He got 48 V across certain pairs but who knows for sure.



> Is this a heat/cool system or heat only?


Heat pump so it was a heat/cool T-stat



> And last but not least what all had to replaced to get the furnace running.


 It isn't running yet, as far as I know. He did look at the wire in the unit and traced it all the way to the T-stat. No problems at all.

Heating guy is next in line- after the insurance company etc.


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## Charlie K (Aug 14, 2008)

Let us know when the HVAC guys get done. I am curious to find out. Thanks.

Charlie


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## MDShunk (Jan 7, 2007)

24 volt hvac transformers don't generally have PTC thermal overload fuses wound in them until they get 250va and bigger. Even at that, few of them have it. 

I see two possible scenarios creating 46 volts on the secondary:
1) Turn to turn short changing the turns ratio, or plain old primary-secondary fault creating an autotransformer.
2) Two transformers (one in heating equipment and one in ac equipment) connected to the same control circuit. If they aren't co-phased well, they can actually boost the RMS voltage measured (or, buck each other and get hot and burn up themselves).


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## guest (Feb 21, 2009)

Dennis, wonder if the 'stat in this fire was one of the ones being recalled:

http://www.cpsc.gov/cpscpub/prerel/prhtml11/11096.html




> *Name of Product: *Programmable thermostats
> *Units: *About 180,000 in the United States and 8,300 in Canada
> *Manufacturer: *White-Rodgers of St. Louis, Mo.
> *Hazard: *The programmable thermostats constantly charge the backup AA batteries used to power the thermostat's clock. This can cause the batteries to leak, resulting in a fire hazard.
> ...


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## Shockdoc (Mar 4, 2010)

I ha d a HO that had a old style LV one arcing in his daughters room, I can see how they can ignite , better watch out the NFPA catches wind of this furnaces will soon have to be AFCI protected and manufacturers will need to come out with a 24 volt AFCI for thermostats which will be the responsibility of the installer to purchase and install instead of the manufacturer of unit.


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## sparks134 (Jan 30, 2009)

mxslick said:


> Dennis, wonder if the 'stat in this fire was one of the ones being recalled:
> 
> http://www.cpsc.gov/cpscpub/prerel/prhtml11/11096.html


Sh!&$...I have one of those in my house, but it's not the programable one.


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## Dennis Alwon (May 9, 2009)

I just spoke with the homeowner. The thermostat was a Honeywell not White - Rodgers.

Apparently the problem was at the compressor. According to the HVAC guys the compressor went bad and the high voltage wire came in contact with the low voltage wire. At least this is there diagnosis- I have not seen it so that's all I got. Now how did the low voltage cable come into contact with the HV cable is another question and why 46V and not 120v or more. 

Maybe someone can answer this-- if one leg of the 240V circuit touched one wire on the thermostat would it be possible that there was 120 to ground but 46V across the T-stat conductors?


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## Wirenuting (Sep 12, 2010)

Dennis Alwon said:


> I just spoke with the homeowner. The thermostat was a Honeywell not White - Rodgers.
> 
> Apparently the problem was at the compressor. According to the HVAC guys the compressor went bad and the high voltage wire came in contact with the low voltage wire. At least this is there diagnosis- I have not seen it so that's all I got. Now how did the low voltage cable come into contact with the HV cable is another question and why 46V and not 120v or more.
> 
> Maybe someone can answer this-- if one leg of the 240V circuit touched one wire on the thermostat would it be possible that there was 120 to ground but 46V across the T-stat conductors?


The only time I have seen LV being near enough to the LV is the internal o/l inside the AC compressor. But that should fail open as it heated & the compressor would have been running while it happened. 
The OCP should have tripped before the surge got that far. The LV also closes the contactor outside in the AC unit. If it has a HP or LP cut out, they normally are not near enough to cause a fault. 
The only other place LV & HV come together in on the furnace PC board. Since this is 5 years old it should have failed or burnt open at the board. 

If it was a heat pump then I don't know how they are wired. But would think pretty much the same.


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## Dennis Alwon (May 9, 2009)

It was a heat pump.


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## Ranger2001 (Jan 12, 2011)

I just want to thank Dennis A. for his post on the thermostat catching fire.
And thanks for the pictures. It people like you, that make come back time to 
time to read new posts.


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## kevmanTA (Jul 20, 2010)

They need some zener diodes..


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## Wirenuting (Sep 12, 2010)

kevmanTA said:


> They need some zener diodes..


But what happens when they avalanche?


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## Dennis Alwon (May 9, 2009)

Ranger2001 said:


> I just want to thank Dennis A. for his post on the thermostat catching fire.
> And thanks for the pictures. It people like you, that make come back time to
> time to read new posts.


Thank you and welcome to the forum.


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## Shockdoc (Mar 4, 2010)

Proposition 1100 A NFPA - 24 volt transformers shall incorporate AFCI protection for secondary leads.:jester:


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## frenchelectrican (Mar 15, 2007)

Dennis Alwon said:


> I just spoke with the homeowner. The thermostat was a Honeywell not White - Rodgers.
> 
> Apparently the problem was at the compressor. According to the HVAC guys the compressor went bad and the high voltage wire came in contact with the low voltage wire. At least this is there diagnosis- I have not seen it so that's all I got. Now how did the low voltage cable come into contact with the HV cable is another question and why 46V and not 120v or more.
> 
> Maybe someone can answer this-- if one leg of the 240V circuit touched one wire on the thermostat would it be possible that there was 120 to ground but 46V across the T-stat conductors?


 
Dennis.,
I will try this kind of experment to see what I can come up with this.

I am not sure if I did catch someone mention what brand name this heat pump unit is. 

But I know Carrier and some York units they have open compartment so that possiblty it can happend.

I will let you know the result in a day or two when I get my free time at night time.

Merci.
Marc


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## Dennis Alwon (May 9, 2009)

frenchelectrican said:


> Dennis.,
> I will try this kind of experment to see what I can come up with this.
> Merci.
> Marc


Don't blow yourself up on my account.


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## frenchelectrican (Mar 15, 2007)

Dennis Alwon said:


> Don't blow yourself up on my account.


I did ran the test and it did not match up to your situation and it was much worst than I expected.

I came up 185 volts one way and I try to reverse it and still the same but will do couple more test in little bit after I get couple more small cartage fuse.

Keep in your mind I did put a current limiting restitours in there so it will not go crazy with it.

Just engough to read the voltage but nothing more above that.

Merci.
Marc


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## nrp3 (Jan 24, 2009)

A heat pump thermostat is different than one used for say gas forced hot air or a boiler I believe. The other thing I wonder about, was this a powered thermostat in that did it carry the other half of the transformer ie 'c' or common? If not and it was just switching the 'r' or one half of the transformer, why would it matter whether it was 24v or even 48v?


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## guest (Feb 21, 2009)

sparks134 said:


> Sh!&$...I have one of those in my house, but it's not the programable one.


To be safe click on the recall link and check you model and date codes against the recall. 



Dennis Alwon said:


> I just spoke with the homeowner. The thermostat was a Honeywell not White - Rodgers.
> 
> Apparently the problem was at the compressor. According to the HVAC guys the *compressor went bad and the high voltage wire came in contact with the low voltage wire.* At least this is there diagnosis- I have not seen it so that's all I got. * Now how did the low voltage cable come into contact with the HV cable is another question* and why 46V and not 120v or more.
> 
> Maybe someone can answer this-- if one leg of the 240V circuit touched one wire on the thermostat would it be possible that there was 120 to ground but 46V across the T-stat conductors?


My bulls**t meter is pegged on this one...I have seen and messed with literally hundreds of A/C and heat pump units and the wiring is generally not set up in a way to allow what they describe. 

Now the possibilities I see are:

1: Contactor for compressor had a total melt down, which _MIGHT_ allow the HV wire from the contacts to come in contact with the wiring to the coil (which is 24v).
2: Wiring to the unit burned up and melted, which could be in contact (intentionally or accidentally) with the LV cable. But the overload in the compressor should have opened before the wiring burned. Same for the OCPD..if properly sized it should open before internal wiring damage. 

A mere compressor failure, in my experience anyway, has NEVER resulted in anything other than a fried compressor and arced-up contacts on the contactor.

I am with those who stated a failure of the control transformer....a short in the primary could easily result in double the voltage. 

I think there are some facts missing here...


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## Dennis Alwon (May 9, 2009)

mxslick said:


> My bulls**t meter is pegged on this one...I have seen and messed with literally hundreds of A/C and heat pump units and the wiring is generally not set up in a way to allow what they describe.


Rember the info I gave came from the HO. She may have gotten the facts wrong. It may have very well been the contactor.


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## kevmanTA (Jul 20, 2010)

Wirenuting said:


> But what happens when they avalanche?


You run!!


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## Wirenuting (Sep 12, 2010)

kevmanTA said:


> You run!!


The light or flight reflex.


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## m&pc9 (Jan 26, 2011)

I am a HVAC tech and on tuesday I had the same problem.




















I do not know what caused the fire. I changed the thermostat and the transformer, I added a 5amp fuse to the transformer to help prevent this again. I inspected the thermostat wire and the wiring inside the heat pump. The unit was working properly after I changed the parts out.

It was a heat pump and had a mercury thermostat.

The blower relay was bad also but I dont think it had anything to do with the fire.

I think the transformer shorted out and sent high voltage in to the thermostat.


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## Dennis Alwon (May 9, 2009)

Do you know what brand it was. As stated earlier White and Rogers have had problems.


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## m&pc9 (Jan 26, 2011)

I believe it to be a Janatrol brand just by the appearance.

I think white rogers may have made them, but Im unsure. The unit was a 1999 model and I think the thermostat was installed then.


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## Roadhouse (Oct 16, 2010)

If high voltage from a component came in contact with the low voltage wire such as one leg of 120 at the compressor than the control board at the furnace (inside of unit) which feed both power through a transformer to the stat, from high to low, would blow, not the stat. 

all power is taken through and from the control board. stat is powered from board, tells board which mode to go in equaling which voltage, high and low, to send where such as in to heat pump (condensor) or to blower or to what. the condensor has it's own high voltage which only makes contact to compressor via low voltage pulling in the contactor by way of stat being powered through board telling board where to send low voltage and around and around we go.

this is a case of the step down transformer simply going out.

stats are placed near return airs and mainly the central one which would not be in a bedroom.


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## Wirenuting (Sep 12, 2010)

Roadhouse said:


> stats are placed near return airs and mainly the central one which would not be in a bedroom.


They get placed near the return air if the installer is smart. 
Most times they are just landed on a north or east facing interior wall.

Roadhouse,, have you or your coworkers ever see a stat burn like that?
None of mine have.


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## Roadhouse (Oct 16, 2010)

I have never witnessed a stat burn up, can't say about anyone I've ever worked with throughout my 12 years, though.

Now I have pulled the low voltage wire on a condensing unit that was calling for cool (manually ending the low voltage signal at the contactor instead of at the stat) and accidentally let it touch the high side of the contactor and the board blew instantly.


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## Roadhouse (Oct 16, 2010)

Wirenuting said:


> They get placed near the return air if the installer is smart.
> Most times they are just landed on a north or east facing interior wall.


 
That just sounds so wrong. We sure these are not zoned systems with multiple stats?


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## m&pc9 (Jan 26, 2011)

The one I worked on was not zoned.


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## Roadhouse (Oct 16, 2010)

Roadhouse said:


> I have never witnessed a stat burn up, can't say about anyone I've ever worked with throughout my 12 years, though.
> 
> Now I have pulled the low voltage wire on a condensing unit that was calling for cool (manually ending the low voltage signal at the contactor instead of at the stat) and accidentally let it touch the high side of the contactor and the board blew instantly.


Now had I turned the call for cool off at the stat then the control board would not have sent 24v to the contactor which it had when I pulled it off of the contactor but regardless of if 24v was present, 120 backfeeding through the low voltage control wire to the board will fry the board. 

You guys should try it sometime.  

Again, the call is through the board, the stat only tells it to do it's job, control components by way of which voltage to send where, high and/or low.


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## Wirenuting (Sep 12, 2010)

Roadhouse said:


> That just sounds so wrong. We sure these are not zoned systems with multiple stats?


Ya I'm sure they are not zoned. 
It's just what I've seen over the years. 

As for shorting out stat wires,, couple years ago I was drilling down thru my wall for an extra recpt that my wife wanted. I was below my thermostat. I was sure I would miss it. 
Few minutes later my son asked me why the AC compressor was chattering outside. 

Well,, I missed the wire in the wall,, but hit it dead center in the basement ceiling.


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## Roadhouse (Oct 16, 2010)

example: turn heat on on a heat pump system at stat. 

24 volts through control board will be sent to the reversing valve at heat pump so refrigerant can flow in reverse direction while 24 volts is pulling in the contactor allowing for the heat pump's own 240 volt circuit to pass through the contactor to turn on compressor while the board is now sending 120 volts to the blower motor in the furnace on what should be low speed for heat through the boards motor controlling speed tap and whoala!, heat is on by way of someone setting the stat which controls the board into heat mode.

Man, I enjoy my work.


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## Roadhouse (Oct 16, 2010)

Wirenuting said:


> Ya I'm sure they are not zoned.
> It's just what I've seen over the years.
> 
> As for shorting out stat wires,, couple years ago I was drilling down thru my wall for an extra recpt that my wife wanted. I was below my thermostat. I was sure I would miss it.
> ...


 
On the low voltage side of things such as in the case of two low voltage wires touching one anther and voltage being sent back the wrong way, the control board is protected via usually a 3 or a 5 amp fuse, for these types of situations. It happens all the time.

Home owner: "My a/c doesn't work."

Me: "How much money you willing to spend for my time?" 

Get over there and the fuse is blown on the control board in the furnace.

Me: "M'am, have you recently hung up any new pictures?"

Home owner: "Yes, over there." 

Me: "That'll be 10 grand, thank you very much."


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## Wirenuting (Sep 12, 2010)

Roadhouse said:


> On the low voltage side of things such as in the case of two low voltage wires touching one anther and voltage being sent back the wrong way, the control board is protected via usually a 3 or a 5 amp fuse, for these types of situations. It happens all the time.
> 
> Home owner: "My a/c doesn't work."
> 
> ...


10k? 
LoL,, I'll show you the door.


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## Roadhouse (Oct 16, 2010)

Wirenuting said:


> 10k?
> LoL,, I'll show you the door.


 
right. nah, if it's an immediate fix meaning one of those you have a hunch and get it right on the button within a few minutes and takes no real material to speak of other than perhaps a few tiny low control voltage wire nuts and maybe one fuse, it's just the service call fee.

Maybe if I advertise "Male hunk service tech, will diagnose and repair while naked" I could make a gazillion dollars from those old and rich, divorced women in need of some stud lovin'. 

Hey, I've got a new business strategy..


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## m&pc9 (Jan 26, 2011)

Roadhouse said:


> example: turn heat on on a heat pump system at stat.
> 
> 24 volts through control board will be sent to the reversing valve at heat pump so refrigerant can flow in reverse direction while 24 volts is pulling in the contactor allowing for the heat pump's own 240 volt circuit to pass through the contactor to turn on compressor while the board is now sending 120 volts to the blower motor in the furnace on what should be low speed for heat through the boards motor controlling speed tap and whoala!, heat is on by way of someone setting the stat which controls the board into heat mode.
> 
> Man, I enjoy my work.



For 1 most heat pumps send power to the reversing valve when in cooling, Very few do it in the heating. All heat pumps use 240 volt blower motors because they must use electric heat to help out in the cold months and during the defrost cycle. Most heat pumps do not use a control board the thermostat sends power to the blower relay to turn on the blower. It also sends power to the contactor to turn on the compressor. 

You must be talking about a gas furnace which has a control board to control the blower. But the thermostat still controls the heat pump.

You may want to learn more about your job before you enjoy it so much.


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## Roadhouse (Oct 16, 2010)

m&pc9 said:


> For 1 most heat pumps send power to the reversing valve when in cooling, Very few do it in the heating. All heat pumps use 240 volt blower motors because they must use electric heat to help out in the cold months and during the defrost cycle. Most heat pumps do not use a control board the thermostat sends power to the blower relay to turn on the blower. It also sends power to the contactor to turn on the compressor.
> 
> You must be talking about a gas furnace which has a control board to control the blower. But the thermostat still controls the heat pump.
> 
> You may want to learn more about your job before you enjoy it so much.


Anyone have any ketchup, my foot tastes a little bland and dry. :whistling2:

I knew it was one the other, heat or cool. Either way it needs to be reversed for each operation regardless of in which operating mode it is being told to switch.

You must be correct with the rest as well. Eh, you win some you lose some.


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## Roadhouse (Oct 16, 2010)

Btw, are you saying that the blower motor itself runs on 240?


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## Roadhouse (Oct 16, 2010)

*heat pump*

"The fan control board receives control voltage from the thermostat and in turn supplies power to the blower motor to operate it in either high or low speed."


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## Roadhouse (Oct 16, 2010)

I honestly don't know what else there could be to tell the blower, 120 or 240 as there are both, to come on in low speed for heat or high speed for cool other than a control board.


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## m&pc9 (Jan 26, 2011)

Roadhouse said:


> I honestly don't know what else there could be to tell the blower, 120 or 240 as there are both, to come on in low speed for heat or high speed for cool other than a control board.



On a heat pump Its just a relay. The motor is 240 volts.


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## m&pc9 (Jan 26, 2011)

A furnace runs on 120 volts, But an air handler (which is hooked to a heat pump) runs on 240 volts.


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## Dennis Alwon (May 9, 2009)

m&pc9 said:


> A furnace runs on 120 volts, But an air handler (which is hooked to a heat pump) runs on 240 volts.


I agree but there are a few split units systems that run on 120V. I wired an outdoor heat pump as I always do and I never checked the voltage-- It was a 120V unit. I got it before it did any damage- not sure how it didn't blow everything out but I had 240v wired to it.


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## Roadhouse (Oct 16, 2010)

I know the voltage and set up requirements for each, thanks. Obviously there is no need for gas plus refrigerant first stage heat and electrical heat strips as auxilary and down here in Houston we have air handlers for both first and secondary heat. No gas furnace or reversed refrigerant flow for heat heat pumps. 

Air handler covers all heat, electrical only, and condensing unit for cool only, in an air handler install. 

I was unaware of the relay for heat pumps, though.


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## Roadhouse (Oct 16, 2010)

Can you explain the relay and what voltage and how it's receving it's call? Somethingi s telling the relay to open and close so that would be the call from a control board, right?

and for your viewing pleasure, a two ton 120 v gas furnace in my living room:


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## Roadhouse (Oct 16, 2010)

*fun fact*

check out the two vertical pieces of metal, the heat exchanger. in this furnace it has two chambers making up the heat exchanger for btu output. if that output needed to be higher for a home that loses more heat per hour then what this home did for it's application and needs than there would be three chambers with flames being pulled through them so the same furnace with a different and higher btu so different furnace...but the same...yet different.


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## Roadhouse (Oct 16, 2010)

The low voltage wires that should be hooked to the low voltage strip, there are no low voltage wires connected as this unit has been taken out and so I am controlling it with jumpers at the board, on the lower left hand is low voltage center of the board. The red light on means this thing is powered up, btw.

the red, blue and the black wires are the high voltage to the blower on the high voltage side of the control board and for heat it will be the lower speed tap and for the cool the higher speed tap and then for med-high or med-low and those can be "parked" on the board.


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## Roadhouse (Oct 16, 2010)

m&pc9 said:


> For 1 most heat pumps send power to the reversing valve when in cooling, Very few do it in the heating. All heat pumps use 240 volt blower motors because they must use electric heat to help out in the cold months and during the defrost cycle. Most heat pumps do not use a control board the thermostat sends power to the blower relay to turn on the blower. It also sends power to the contactor to turn on the compressor.
> 
> You must be talking about a gas furnace which has a control board to control the blower. But the thermostat still controls the heat pump.
> 
> You may want to learn more about your job before you enjoy it so much.


I'm still waiting for you to tell me, first of all, exactly how it is a heat pump works without a control board, that control board obviously meaning the air handler has no control board as that is where control boards are so no t-stat either as there's no need for it to control anything so how exactly does this work? Telepathy perhaps turns on a relay?

Please enlighten me.


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## m&pc9 (Jan 26, 2011)

Roadhouse said:


> I'm still waiting for you to tell me, first of all, exactly how it is a heat pump works without a control board, that control board obviously meaning the air handler has no control board as that is where control boards are so no t-stat either as there's no need for it to control anything so how exactly does this work? Telepathy perhaps turns on a relay?
> 
> Please enlighten me.



The thermostat does all the work. In heat it will send power to the compressor contactor and the fan relay. And when it needs the second stage it sends power to the heat sequencer to turn on the electric heat.

Even in a furnace the thermostat still works the condenser.


The newer thermostats are going to use telepathy.


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## m&pc9 (Jan 26, 2011)

Dennis Alwon said:


> I agree but there are a few split units systems that run on 120V. I wired an outdoor heat pump as I always do and I never checked the voltage-- It was a 120V unit. I got it before it did any damage- not sure how it didn't blow everything out but I had 240v wired to it.




Im sure over the years they have tried alot of different designs.

Some ductless splits run on 120v.


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## m&pc9 (Jan 26, 2011)

Roadhouse said:


> Can you explain the relay and what voltage and how it's receving it's call? Somethingi s telling the relay to open and close so that would be the call from a control board, right?
> 
> and for your viewing pleasure, a two ton 120 v gas furnace in my living room:



That is not a heat pump. 


That is a gas furnace.


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## Roadhouse (Oct 16, 2010)

I never would have imagined that being a gas furnace what with having to disconnect the gas line when I was removing it from an attic last week and pulling the exchanger from it and then reconnecting the gas to the new what I guess now I thought was an air handler. Hmm, so you mean air handlers do not have draft inducer motors and ignitors and flame sensors and gas lines to them? Hmmm, I never knew the difference. Really, that is a gas furnace? No wonder it had a flue pipe too! 

Not that I haven't installed a few hundred furnaces and a few hundred air handlers up to tonnoges bigger than your home but thanks, I never knew the difference until you pointed that out. All these years, damn.

Thanks pal, you're swell.


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## Roadhouse (Oct 16, 2010)

m&pc9 said:


> The thermostat does all the work. In heat it will send power to the compressor contactor and the fan relay. And when it needs the second stage it sends power to the heat sequencer to turn on the electric heat.
> 
> Even in a furnace the thermostat still works the condenser.
> 
> ...


What planet are you from? Nothing works without a control board. All heating and cooling terminals are there.


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## Roadhouse (Oct 16, 2010)

Well, that was amusing.


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## Roadhouse (Oct 16, 2010)

I'll take some pics of the whatever off Carrier brand, either Payne or Bryant, heat pump that I installed at my sisters home some many years ago and post them but don't be surprised when the control board shows itself. I mean, I didn't just go and add that in, the system needed something to control the signal from the stat and I do believe Carrier knew that ahead of time.

Maybe they just put this one control board in for little old me?..


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## Roadhouse (Oct 16, 2010)

Okay, I thought a bit more about it and I see where you are coming from. Yes, there are relays and switches as you wire nut them to the stat wires in air handlers vs. a furnace with terminals on the control board. Not saying you are completely right or wrong, just not saying you are completely right for certain. 

Damn it. :whistling2:


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## Roadhouse (Oct 16, 2010)

*7.5 ton Rheem air handler*










and the condensor for the air handler on the far left, American Standard









and the heat kit with a CONTROL strip.


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## Roadhouse (Oct 16, 2010)

The service call on that air handler was that it was not doing anything, heating or cooling. The wire from the transformer to the control strip was broken so in turn the stat could not tell anything to come on as it had no power through the control.

Outside of that control strip I do believe you are right, no real control board such as on a furnace outside of the stat.


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## Roadhouse (Oct 16, 2010)

four words: internal logic control board.

Thanks Lusker, Ken. 

Dennis, sorry for hijacking your thread. :blink:


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## guest (Feb 21, 2009)

Roadhouse, you are both right and also very wrong!! In residential at least, furnaces and A/C units did NOT have "internal control or logic boards" for MANY years. It was direct connection for the 'stat to the contactor in the condenser, fan relay and gas valve or heat strip contactor (thru some safety devices in many cases of course.) The furnace and central A/C I installed at my house in Norwalk back in the mid 80's had no control boards of any kind. 

There are a lot of older units out there still in service, and it is possible that the unit in this fire incident was an older one.


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## Dennis Alwon (May 9, 2009)

Roadhouse said:


> four words: internal logic control board.
> 
> Thanks Lusker, Ken.
> 
> Dennis, sorry for hijacking your thread. :blink:


No problem, as long as someone is learning from it, I am good with it.


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## Roadhouse (Oct 16, 2010)

mxslick said:


> Roadhouse, you are both right and also very wrong!! In residential at least, furnaces and A/C units did NOT have "internal control or logic boards" for MANY years. It was direct connection for the 'stat to the contactor in the condenser, fan relay and gas valve or heat strip contactor (thru some safety devices in many cases of course.) The furnace and central A/C I installed at my house in Norwalk back in the mid 80's had no control boards of any kind.
> 
> There are a lot of older units out there still in service, and it is possible that the unit in this fire incident was an older one.


I was grasping desperately for air, I thought everyone could tell that. Yes, I realize I was both right and wrong, the terminal strip on that Rheem being the closest thing to a control strip on those older versions you are talking about, the stat itself being the board such as how my new *arch nemesis* on here has suggested. 

And then the biggest HVACR gun of them all opened up Pandora's Box with exactly how the internal logic control board on the newer and newest air handlers handle everything with their internal logic control boards and still to date the stat is nothing more than a switch. There is a board at each piece of equipment especially in heat pumps, but it's the internal logic control board in the air handler directing traffic by way of switch, again that high tech simpleton switch being merely the thermostat.

*


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## Roadhouse (Oct 16, 2010)

Dennis Alwon said:


> No problem, as long as someone is learning from it, I am good with it.


I sure did, thanks.


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## Englishsparky (Nov 6, 2010)

I didnt really touch a/c or gas furnaces in the UK, except wiring the supplies for them.


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## m&pc9 (Jan 26, 2011)

Roadhouse said:


> and the condensor for the air handler on the far left, American Standard



That one looks like a Goodman to me.



I dont want to argue with any one. I just wanted to post the pics of my thermostat fire. Because it looked so much like the OPs.

I know there are so many different brands of heat pumps and so many different configurations of ways of operating that we were both right. There is no black and white in the industry.


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## Roadhouse (Oct 16, 2010)

Hey man, no worries and sorry for acting a bit of a fool. I enjoy hvacr and enjoy having someone else who knows about it to debate with.

And I am no heat pump pro. Here in Houston we don't have very many of them, I've personally only installed two heat pump systems in over a decade so that pretty much sums up my experience with them. I'm always learning more and more about hvacr.

Anywho, no arguements. It's all good.


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## Roadhouse (Oct 16, 2010)

The next time I go back out to that job I'll double check to see what the make of the condensing unit is. You might be right, I didn't really pay attention outside of if it was getting it's call for cool along with the 460 3 phase high voltage. It was after I found the problem in the air handler.


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## Angf (May 14, 2018)

This happened to my mothers House last night when she turned on the boiler to warm up the house the thermostat went up in flames it was replaced over a year ago with a digital thermostat from home depot . Thank god the house didn't go up in flames and what's really troubling is that the fire alarms didn't go off and they all have fresh batteries.


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## Bird dog (Oct 27, 2015)

Angf said:


> This happened to my mothers House last night when she turned on the boiler to warm up the house the thermostat went up in flames it was replaced over a year ago with a digital thermostat from home depot . Thank god the house didn't go up in flames and what's really troubling is that the fire alarms didn't go off and they all have fresh batteries.



Please fill out your profile.


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## Dennis Alwon (May 9, 2009)

Wow, that thread is 7 years old. I had forgotten about that. Looks like you got lucky no one got hurt and the house is still there


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## Bird dog (Oct 27, 2015)

Angf said:


> This happened to my mothers House last night when she turned on the boiler to warm up the house the thermostat went up in flames it was replaced over a year ago with a digital thermostat from home depot . Thank god the house didn't go up in flames and what's really troubling is that the fire alarms didn't go off and they all have fresh batteries.



What kind of smoke detectors are they & where were they located? That really is concerning that they didn't go off.


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## frenchelectrican (Mar 15, 2007)

Bird dog said:


> What kind of smoke detectors are they & where were they located? That really is concerning that they didn't go off.


I been wondering too .,

If the OP's smoke detectors are more than 10 years old they are pretty much useless.


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## Wirenuting (Sep 12, 2010)

Angf said:


> This happened to my mothers House last night when she turned on the boiler to warm up the house the thermostat went up in flames it was replaced over a year ago with a digital thermostat from home depot .
> 
> Thank god the house didn't go up in flames and what's really troubling is that the fire alarms didn't go off and they all have fresh batteries.


Can you tell us what brand and model of thermostat that was?
Have you reported it to your insurance company?

Can you tell us how old the smoke detector is and were is is mounted?
Correct placement of a smoke detector is essential if you want it to work correctly. To close to a wall or corner and it can’t sense the smoke.


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## MDShunk (Jan 7, 2007)

My own house has 11 smoke detectors. I figure at least one of them ought to trigger f there's a fire. I'm not super concerned about my stuff burning up, but I'd like to get out before I burn up.


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> What kind of smoke detectors are they & where were they located? That really is concerning that they didn't go off.


Maybe the ones that have the recall going on.


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## numbers (Dec 23, 2011)

I once had a service call, people were getting shocked when they pressed the doorbell button. It was a defective doorbell transformer.


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