# Resolving a flickering light issue



## DEA (Dec 13, 2008)

The house has a 200 amp service with two 100 amp sub-panels. The master bath was just remodeled using an electric 240v water heater that was assumed to shut off once the hot water from the existing water tank reached the shower. However, the electric heater cycles instead of shutting off, which is causing the lights in the bathroom to flicker.

The electric heater is on a 40 amp dedicated line to the same sub-panel that services power to the lights in the bathroom. Any thoughts on if moving the lights or heater to the second sub-panel (so that they were on separate sub-panels) would help resolve the issue? If not, what would be the next logical step?

Thanks!


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## Speedy Petey (Jan 10, 2007)

I have had the exact same thing with one of those stupid point-of-use insta-hot water heaters. In fact no solution was found so far. The lights flicker rapidly and noticeably. 

Are you the electrician who wired it? Is the circuit sized properly?


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## BryanMD (Dec 31, 2007)

"The master bath was just remodeled..."

Start with the simple stuff. It worked ok before someone was in there poking and pulling right? I'd start with what was in the way of his work that he (inadvertently) disturbed. Bet you find a loose connection on the other end of the romex that he had to get past.


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## DEA (Dec 13, 2008)

The electric heater was added during the remodel (which my coworkers and I did). The master bathroom is the furthest water usage point from the gas water heater, so the complaint was of having to wait a long time for hot water to reach the shower. After looking into various solutions, the POU electric heater seemed to be the best option. My understanding was that it would shut itself off after the hot water reached the electric heater. It is possible that adjustments on the internal electronics may get the electric heater to shut off rather than cycle, but support information for the heater has been difficult to find so far.

I understand that a cycling 40a circuit is going to put a strain on the panel, but I am not sure if it would also affect the second 100a panel. I can check to see if other lights in the house (serviced by the second panel) also flicker. If not, then moving the master bathroom lights to the second panel may be the easiest solution.


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## Kevin J (Dec 11, 2008)

Was the new point of use water heater hooked up in series with the existing hot water lines? Generally, these water heaters turn on when a flow of water is detected, not by temperature of the incoming water. If this is the case in said hook-up, then the POU heater is not installed for the best application. Have you considered a re-circulator pump on the existing water heater to make sure hot water is always in the new bath? If so, then you might not need the new POU heater.


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## DEA (Dec 13, 2008)

Correct, the POU heater is hooked up in series with the hot water line at the shower. It does turn on when flow is detected, and begins to cycle on/off at various rates depending on the hot water temperature in the line. My understanding was that this unit would stay off once the water temp exceeded the temperature that it is heating to, but it does not. It is possible that it just needs an adjustment, or that it does not, in-fact, ever turn completely off when flow is still detected. If the latter is true, then the light flickering is a potential issue that people should consider before installing a unit like this.

I have installed various types of recirculation pump systems (both at the water tank and below the vanity sink) but they each have different limitations/drawbacks as well. Since the walls were already open for the plumbing, I decided to try the in-line electric heater. It does work quite well, with the exception of the flickering lights. If it is not possible to get the unit to stop cycling on/off while the water is flowing, then hopefully moving the bathroom lights to the second panel will alleviate the issue. I was just curious if a cycling 40a circuit could affect voltage at both panels.

Thanks!
Dave


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## gilbequick (Oct 6, 2007)

Kevin J said:


> Was the new point of use water heater hooked up in series with the existing hot water lines? Generally, these water heaters turn on when a flow of water is detected, not by temperature of the incoming water. If this is the case in said hook-up, then the POU heater is not installed for the best application. Have you considered a re-circulator pump on the existing water heater to make sure hot water is always in the new bath? If so, then you might not need the new POU heater.


In order to correctly install the recirc pump don't you need to run a water line from the furthest water fixture back to the water heater? You'd need a plumber for that, and then all you'd have to do is hook up a 120v line to the recirc pump which only draws a small load.


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## DEA (Dec 13, 2008)

gilbequick said:


> In order to correctly install the recirc pump don't you need to run a water line from the furthest water fixture back to the water heater? You'd need a plumber for that, and then all you'd have to do is hook up a 120v line to the recirc pump which only draws a small load.


The under-vanity type that I have installed use a manifold/valve setup that allows the pump to pull water down the hot line and push it back to the tank via the cold line. Once hot water is detected, the pump shuts off. The downside to this is the noise and space related to the pump system installed in the vanity. These can be set up to run on a timer (have it run just before you get up in the morning, etc) or with a small button that you push when you are ready for some hot water. These use basic supply-line fittings, so nothing more than a wrench and a under-vanity outlet are needed.

The type that use the pump at the tank do the same thing, but since it does not detect the hot water until it has made a complete loop, basically all the water in the existing cold lines will be warmed in the process (until the pump shuts off and cold water is used). I have only seen this system used with a timer. These may require sweat solder connections, so if you are not comfortable with those, a plumber may be needed for that.

HTH,
Dave


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## BryanMD (Dec 31, 2007)

DEA said:


> The under-vanity type that I have installed use a manifold/valve setup that allows the pump to pull water down the hot line and push it back to the tank via the cold line.


 I'm no plumber but I don't see how that can meet their codes let alone being at the next sink trying to get some cold water.

(just a comment)

So... anyone sorted out the cause of the flickering lights yet?


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## waco (Dec 10, 2007)

Before I did much changing in the panels, I think I'd first use a voltmeter to see if the fluctuation is effecting both panels. Then, I'd try moving the breaker for the POU water heater to the top of the buss or at least far away from the breaker for the branch circuit the lights are on.

But I'd first see if the voltage drop is unique to the one panel or common to them both.


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## gilbequick (Oct 6, 2007)

DEA said:


> The type that use the pump at the tank do the same thing, but since it does not detect the hot water until it has made a complete loop, basically all the water in the existing cold lines will be warmed in the process (until the pump shuts off and cold water is used). I have only seen this system used with a timer. These may require sweat solder connections, so if you are not comfortable with those, a plumber may be needed for that.
> 
> HTH,
> Dave


No what I'm talking about is not a point of use unit but a whole house unit. The way this works is you create a loop with your hot water line starting from your hot water heater and ending at your hot water heater. The recirculating pump continuously recirculates hot water throughout the hot water line only (you don't use the cold line at all) so it's there when you want it. The pump itself pulls very little power at all. You save thousands of gallons of water a year not waiting for hot water to come out and money on your water bill. 

I mention this because it might be an option to the homeowners if they definitely want to get rid of the flickering lights. Instead of the POU unit pulling 12A plus, the recirc pump might pull 1A.


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## 480sparky (Sep 20, 2007)

gilbequick said:


> No what I'm talking about is not a point of use unit but a whole house unit. ......


Very similar to units used in commercial. Hotels/motels are common uses. Water heater in mechanical room, but someone way down at the end of the hall still has hot water coursing through the pipe right outside their room. They don't need to wait half an hour for hot water. If the water isn't used, it's recirculated (hence, a recirculating pump) brings it back to the heater, where it's heated back up to temp.

I've done some of these even in custom homes.


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## jbfan (Jan 22, 2007)

I think you are missing the point. The pou water heaters I have seen and installed do not depend on temp to operate, they depend on water flow. 
Also the instructions say not to install inline with a water heater.


You are going to have to correct this problem or the lights will flicker no matter which panel they are fed from.
It is like having a bad contactor on an AC unit, when it chatters, then the lights will flicker as much as they do when the unit starts normally.


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## TheRick (Apr 13, 2008)

jbfan said:


> I think you are missing the point. The pou water heaters I have seen and installed do not depend on temp to operate, they depend on water flow.
> Also the instructions say not to install inline with a water heater.


You get what you pay for! There are models out there that can be used with another heat source, whether it is a water heater or solar collectors, and they do opearte not only on water flow, but also water temperature. They will only heat the water when a preset flowrate is acheived, and will stop heating when the temperature setpoint is acheived and maintained. The key is to know what you or your customer wants out of the unit, and then find the one that will suit that need.


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## Hefty (Oct 17, 2008)

*Free time*

If you have some extra time on your hands, which I'm sure you don't, you could build a temperature control relay circuit and use a Pipe Clip Temperature Sensor. This circuit, once calibrated, would only supply power to the pou heater when the supply water is below a specified amount. I guess this is the same circuitry that you believed was in the pou heater in the first place. I am certainly not an expert, and this may be too much trouble, but it would work.


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