# Testing a Hot Water Tank



## darren79 (Dec 20, 2011)

I have a friend who says her hot water tank is causing her breaker to trip and she wants me to take a look at it.

I do very little service work and have a very simple question. When I check the elements and figure out what the resistance is with math, should that number match when I test with my meter. Lets say I have a 4500W element on 240v, doing the math that would give me 12.8ohms. When I check the element with my meter should it read 12.8ohms.

ALso is there any way to test if the thermostat is going bad.


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## HARRY304E (Sep 15, 2010)

darren79 said:


> I have a friend who says her hot water tank is causing her breaker to trip and she wants me to take a look at it.
> 
> I do very little service work and have a very simple question. When I check the elements and figure out what the resistance is with math, should that number match when I test with my meter. Lets say I have a 4500W element on 240v, doing the math that would give me 12.8ohms. When I check the element with my meter should it read 12.8ohms.
> 
> ALso is there any way to test if the thermostat is going bad.


If it is a line voltage thermostat then it should just switch on or off at it's temprature setting so it sounds like you have a bad element if so replace all of them if there is more than one .


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

Your assumptions are correct about reading resistance, but it doesn't sound like you need to worry about that. It sounds like you need to check for shorts to ground. Still most likely an element gone bad.


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## darren79 (Dec 20, 2011)

Do you need to drain the tank of anything to switch out the elements, is it a hard job to switch them out.


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## JohnR (Apr 12, 2010)

Resistance will be approximately what the math says it should be, no guarantee with that. 

Some reason or other, I have run into a rash of bad WH lately, all of them leakers. "can you fix it?" Yes I can, but I am not licensed to do it, so my insurance won't cover. "Oh".


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## JohnR (Apr 12, 2010)

Yes you better drain the tank. No it is not usually a hard job to switch it out, Make sure if you have the threaded ones, that you use teflon tape, and you use the gasket on the flange type. If you crossthread one of the flange screws you will be getting a new tank.


Oh, and don't turn the power back on, till you have completly refilled the tank.


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## darren79 (Dec 20, 2011)

So the problem was in the fuse holder that was hooked up to the tank, when I went there it was hot to the touch. Got rid of that and put it inside her panel and it is good to go.

When I looked at the tank I saw max 18.75A so I wired it up with #10 and a 30A breaker. After hooking up the tank I tested it to make sure it was working properly and it was pulling 12.3A.

Checked the name plate and it said the elements were 3000W each. Would you wire it to the wattage on the name plate or the max amperage.


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## TOOL_5150 (Aug 27, 2007)

I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


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## MechanicalDVR (Dec 29, 2007)

TOOL_5150 said:


> I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


 
That's fine for a screw in element but the bolt ins can take sometime, especially if the gasket adheres to the take.


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## TooFarFromFenway (Jul 15, 2011)

TOOL_5150 said:


> I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


True, if you've done it a time or two. 

Plus, it most likely hasn't been drained in a while anyway, and cannot hurt it.


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## wcord (Jan 23, 2011)

TOOL_5150 said:


> I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


Obviously the water in your area is soft, or very low in minerals.
In hard water areas, there could be enough calcium buildup to bury the bottom element and then you have a heap of problems getting the element out.
I have a small electric pump that I use to drain the tank, takes maybe 5 minutes to pump it out. Keeps the mess down to a minimum

And when I refill the tank, I don't turn the power back on, until there is no air coming out of a hot water tap. That way you are 100% sure the top element is completely submerged


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## backstay (Feb 3, 2011)

TOOL_5150 said:


> I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


I also change elements without draining.


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## hardworkingstiff (Jan 22, 2007)

JohnR said:


> ... Make sure if you have the threaded ones, that you use teflon tape, ....


?? Since the gasket (even on the threaded ones) makes the leak seal, the tape really doesn't do anything for the seal. Personally, I wouldn't worry about the tape.


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## mrmike (Dec 10, 2010)

JohnR said:


> Yes you better drain the tank. No it is not usually a hard job to switch it out, Make sure if you have the threaded ones, that you use teflon tape, and you use the gasket on the flange type. If you crossthread one of the flange screws you will be getting a new tank.
> 
> 
> Oh, and don't turn the power back on, till you have completly refilled the tank.


 
I have changed out many elements & I have never used teflon tape or seen it on any as there is a rubber seal on the screw in elements that seat against the tank when tight.

Most drain valves don't work anyway as not many people flush their tanks, and they plug up over time so I also don't drain the tank, but make sure I release the pressure before changing one out. 

On another note from above, make sure you run the hot water faucets until the air spurts stop to make sure the tank did fill completely before turning on the breaker..............


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## Southeast Power (Jan 18, 2009)

Usually the element is burned open. Just make sure to change both elements. I try draining them .
Turn off the breaker
Turn off the water supply. Open the bathtub faucet, connect a hose to the tank drain, and 
open the drain valve and the TP valve.
Go buy two new elements and a wrench to fit on them if you do not own one.
Drink two tall boy Budweisers for courage.
Make sure no one turned the breaker back on.
Return to water heater and remove the upper element and replace.

Remove the bottom element. Clean up 5 gallons of water because the tank would not drain.
Install new bottom element.
Close drain valve and TP valve.
Turn on the cold water supply and listed for air to clear pipes. Open all hot water valves one at a time to purge air.

Close all hot water valves.

Turn in breaker.

Pick up tools and check to see if the water is warm.
Check for leaks
Write date on the inside of the covers
Replace covers.

Relieve self of previously consumed Budweiser


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## hardworkingstiff (Jan 22, 2007)

Just a couple more thoughts. I understand the reasons for changing out both elements and don't disagree, but I'd like to make the point that the bottom element does the majority of the work and it will most likely burn out twice (or more) before the top one does. 

As far as draining the tank, I think you are doing a disservice to the customer if you don't drain the tank until the "crud" stops coming out. If that crud ever builds up to the lower element, I believe you will have it going bad often.

For a quick buck, change out the element that's bad (w/out draining the tank) and move on. 

For a little better service (and I'd let the customer decide if they want to spend the extra money), drain the tank (at least the crud) and replace both elements.

All of this of course is just my opinion.


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## aDudeInPhx (Feb 20, 2012)

I helped a friend change out his basement water heater (around here basements in general are very rare). Old 1930s house with very small stairwell. Our biggest concern was emptying it out to make it light enough to drag it up the steep concrete stairs. We bought one of those little $5.95 pumps that hooks to a drill (& then to hoses at both sides) at Home Depot & drained it outside because there was no drain in the basement. It took about 15 minutes but that little pump worked like a charm & was probably the best $5.95 ever spent :thumbup:


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## bobelectric (Feb 24, 2007)

Turn off water supply,lock out power source,try 1 time to remove elements. No go , New tank.


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## backstay (Feb 3, 2011)

hardworkingstiff said:


> Just a couple more thoughts. I understand the reasons for changing out both elements and don't disagree, but I'd like to make the point that the bottom element does the majority of the work and it will most likely burn out twice (or more) before the top one does.
> 
> As far as draining the tank, I think you are doing a disservice to the customer if you don't drain the tank until the "crud" stops coming out. If that crud ever builds up to the lower element, I believe you will have it going bad often.
> 
> ...


Why do you think the bottom element does the most heating? They may or may not burn out more because they are sitting in the mud at the tank bottom. But the top element is wired for priority over the bottom element and should in theory, run more.


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## wcord (Jan 23, 2011)

backstay said:


> Why do you think the bottom element does the most heating? They may or may not burn out more because they are sitting in the mud at the tank bottom. But the top element is wired for priority over the bottom element and should in theory, run more.


The top element only has to heat the upper foot or so of the tank. once the thermostat is satisfied, then the bottom element takes over. The remaining 3 feet of water is heated by the bottom element. Logically, the bottom element should run for 3 times the top element,
In all of the tanks I have repaired, I can only think of 1 top element that was burned out from use. The most common cause was the customer turning on the power before the tank was filled ( big cottage area, so lots of tanks)


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## backstay (Feb 3, 2011)

wcord said:


> The top element only has to heat the upper foot or so of the tank. once the thermostat is satisfied, then the bottom element takes over. The remaining 3 feet of water is heated by the bottom element. Logically, the bottom element should run for 3 times the top element,
> In all of the tanks I have repaired, I can only think of 1 top element that was burned out from use. The most common cause was the customer turning on the power before the tank was filled ( big cottage area, so lots of tanks)


But when using water, it comes off the top. This causes the top element to fire more during those times. 

Even with the bottom sitting in sediment, I don't see a large difference in the amount of bottom element failures over top.


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## sparky970 (Mar 19, 2008)

TOOL_5150 said:


> I wouldnt bother draining the tank. seriously. just be fast about changing the elements and youll be fine. just put a towel down, thats all you need.


Try letting a faucet run when you pull the old one,


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## hardworkingstiff (Jan 22, 2007)

backstay said:


> Why do you think the bottom element does the most heating?





wcord said:


> The top element only has to heat the upper foot or so of the tank. once the thermostat is satisfied, then the bottom element takes over. The remaining 3 feet of water is heated by the bottom element. Logically, the bottom element should run for 3 times the top element,


wcord explained it pretty well but I'd like to add that I believe in most homes the bottom element will run more than 3 times the top. The reason being is as you use hot water the bottom element starts heating and unless you use up enough hot water at one time the top element won't come on and the bottom element will heat the replaced water 100%. I think this scenario is probably the most common, so the top element only really comes on during extremely heavy demand (which is probably not often in most homes). Since it's just me and my wife in our home, I'd be surprised if the top element did any work at all.


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## hardworkingstiff (Jan 22, 2007)

backstay said:


> But when using water, it comes off the top. This causes the top element to fire more during those times.


It's not where the water leaves but where it enters, and it enters into a drop tube down into the bottom of the tank so the cold water entering the tank goes to the bottom (cold water sinks and hot water rises) so as to not reduce the temperature of the hot water stored (near the top) in the tank.


> Even with the bottom sitting in sediment, I don't see a large difference in the amount of bottom element failures over top.


I really find this difficult to believe.


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## backstay (Feb 3, 2011)

hardworkingstiff said:


> It's not where the water leaves but where it enters, and it enters into a drop tube down into the bottom of the tank so the cold water entering the tank goes to the bottom (cold water sinks and hot water rises) so as to not reduce the temperature of the hot water stored (near the top) in the tank.
> 
> I really find this difficult to believe.


Still, I don't change more bottom elements than top.


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