# Tankless Hot water heater causing LEDs to flash



## TMPElectric (Nov 8, 2019)

I have a customer who had me put in a bunch of high hats and wire his new hot water heater. Once we turned on the water heater all the new high hats started to flash. Has anyone ran into this before? I need to figure out a solution to this. 

A couple important things to note

-Its a 200A service
-The water heater takes 3 separate 40A breakers with a max current draw of 112 amps/27Kw! (I have a feeling this is the issue)
-The high hats are dimmable with dimmers that I have paired with the same high hats in the past with no flashing issues. I have the same ones at my house! 

Any help would be appreciated.


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## MikeFL (Apr 16, 2016)

Can you log the dimmer voltage as you run the hot water (causing the heater to come on)?

Some LED's produce a quick flash as the dimming voltage changes.


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## splatz (May 23, 2015)

I'd be surprised if it was anything other than voltage drop. 



You might be able to change the LED drivers for something that tolerates the voltage drop. (You could condition the power on the LED circuit but that could cost a bunch.)


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## Forge Boyz (Nov 7, 2014)

I wired a garage for a guy and he (against my recommendation) got a tankless water heater. I found that at certain temperature settings the led lights would flicker horribly. Adjusting the temperature a degree or two would take care of it. I'm assuming that at certain temp settings matches with certain flow rates would make the element relays kick in and out, causing the flicker. If the elements would come on and stay on the lights would blink on startup, then be fine.

Sent from my SM-G970U1 using Tapatalk


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## splatz (May 23, 2015)

Forge Boyz said:


> I wired a garage for a guy and he (against my recommendation) got a tankless water heater. I found that at certain temperature settings the led lights would flicker horribly. Adjusting the temperature a degree or two would take care of it. I'm assuming that at certain temp settings matches with certain flow rates would make the element relays kick in and out, causing the flicker. If the elements would come on and stay on the lights would blink on startup, then be fine.


I wonder if tweaking the temperature gets the tankless triacs out of step with the LED dimmers ...


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## Forge Boyz (Nov 7, 2014)

It wasn't dimmed lights that had the problem. Nondimmable LED tubes.

Sent from my SM-G970U1 using Tapatalk


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## macmikeman (Jan 23, 2007)

Tankless electric water heaters in N. America are stupid. (unless those little ones under the kitchen sink) Gas ones are fantastic. 

There I said it. Change my mind.


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## TMPElectric (Nov 8, 2019)

I will try to measure the voltage on the dimmer when the HWH is running. They are LED inserts so I don't know how I would change the drivers without changing all the trims and starting over.


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## Mark Devroedt (Oct 2, 2020)

MikeFL said:


> Can you log the dimmer voltage as you run the hot water (causing the heater to come on)?
> 
> Some LED's produce a quick flash as the dimming voltage changes.


Easiest thing to do is swap out that dimmer for a regular switch.CFLs arent dimmable and LEDs might say dimmable but flicker when a heatload pulls in. If the wires on the thermal load are long enough they should be fed off the closest position possible to the main.


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## BillyMac59 (Sep 12, 2019)

A little levity for Friday afternoon....can we call it a cold water heater? I mean, the water going in is cold , right?


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## Wirenuting (Sep 12, 2010)

macmikeman said:


> Tankless electric water heaters in N. America are stupid. (unless those little ones under the kitchen sink) Gas ones are fantastic.
> 
> There I said it. Change my mind.


Gas water heaters cause polar ice melting.

Coal fired heaters are better. The coal dust acts as an insulating blanket and keeps the ice cooler.


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## Dennis Alwon (May 9, 2009)

Of course it will make lights dim... that's a lot of amps for just a water heater. What does the rest of the house use as loads...


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## MHElectric (Oct 14, 2011)

macmikeman said:


> Tankless electric water heaters in N. America are stupid. (unless those little ones under the kitchen sink) Gas ones are fantastic.
> 
> There I said it. Change my mind.


It certainly seems that way.

When you include a 400amp service upgrade, running all the circuits and then wiring everything up, the price for an electric tankless becomes a big obstacle. 

I wish they would come out with a model that only took (1) 60amp circuit, instead of (3) 40amps, and could still keep up with 2 bathrooms and a kitchen.


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## Southeast Power (Jan 18, 2009)

Why the hell would anyone think it’s a good idea to remove a 4.5kw storage tank water heater and replace it with a tankless heater that’s requires 3-40 amp circuits. 25 amps vs 125 amps. You will need an additional 100 amps to operate that heater. It’s No wonder the whole neighborhoods light blink.


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## MHElectric (Oct 14, 2011)

Southeast Power said:


> Why the hell would anyone think it’s a good idea to remove a 4.5kw storage tank water heater and replace it with a tankless heater that’s requires 3-40 amp circuits. 25 amps vs 125 amps. You will need an additional 100 amps to operate that heater. It’s No wonder the whole neighborhoods light blink.


We do a ton of those gas tankless WH, people can't get enough of them. Endless hot water. They love em.

However, between you and...an 80 gallon tank water heater can pump out more hot water than most households will go through at one time. And you don't have to change anything around.

I put one in my house several years ago when there was 6 of us living here and we hardly ever ran out of hot water.


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## daltown5522 (27 d ago)

TMPElectric said:


> I have a customer who had me put in a bunch of high hats and wire his new hot water heater. Once we turned on the water heater all the new high hats started to flash. Has anyone ran into this before? I need to figure out a solution to this. A couple important things to note -Its a 200A service -The water heater takes 3 separate 40A breakers with a max current draw of 112 amps/27Kw! (I have a feeling this is the issue) -The high hats are dimmable with dimmers that I have paired with the same high hats in the past with no flashing issues. I have the same ones at my house! Any help would be appreciated.


 Most of those electrical on demand water heaters uses pulse width modulation (pwm) which causes a signal throughout your electrical system this can cause LED lights to flicker.


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## Almost Retired (Sep 14, 2021)

if you have leds in your house
make sure the FCC has a stamp on the water heater you buy, then read the fine print in the papers to see if it is certified Not to release emi
some of the cheap ones use scr and they are bad bad for leds

if its too late for that you will have to buy better leds


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