# Tankless water heater gets cold after running for a few minutes



## johnmaupin (Nov 30, 2021)

Hi everyone,

I built a home around 2 years ago and decided to go with a tankless water heater instead of a tanked system (honestly a mistake, but I digress).

Every winter…literally this time every year, as soon as it starts to get cooler outside, the water at every faucet will be hot, then get completely cold after around 2-10 minutes (it varies). Sometimes the issue doesn’t happen at all, but I’d say 7/10 it occurs. I can leave the hot water running “, which I’ve tried, and it doesn’t heat up again. I have, however, found that turning everything off, leaving it off for a few minutes, then turning it back on sometimes fixes the issue.
Additionally, if I turn the faucet to half cold water (really sucks when I’m showering…lol) and leave it running for about 30 seconds, it will start to get warmer again slowly, and eventually heat up again.
It is a Rinnai unit, and I’ll be glad to find the model if needed. Nothing else is running when this happens, and the unit was deliberately oversized for the house.


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## johnmaupin (Nov 30, 2021)

I’m not a plumber, but the one who installed our system insisted he sold us an above average heater as sometimes we have lots running at once (not relevant to this issue as it happens even when only a sink is running).
Not sure if this is correct, but I was thinking that since we have very low pressure (35-45 psi) depending on the time of day, perhaps it isn’t getting enough flow, especially if the heater is made for larger, higher flow (I’d assume) applications?


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## johnmaupin (Nov 30, 2021)

Also, forget to add, but turning the hot and cold water off and on rapidly sometimes will fix the issue.


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## goeswiththeflow (Feb 24, 2018)

Awwwe, no fun before he leaves?


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## KCPlumb (Oct 26, 2021)

I really dislike tankless heaters.


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## northplm (Jul 11, 2021)

KCPlumb said:


> I really dislike tankless heaters.


Seems to me like there’s two types of plumbers, ones that think that tankless heaters should be used for every application and that no one should ever install a tank style heater again, and then there’s those that think tankless are the devil. Usually it’s the first group that causes the mindset for the second group. Most tankless issues I see are from guys installing a tankless heater in the wrong application,(usually something with too high of a flow rate), or improper installation leading to problems down the road. Nobody wants to spend money to direct vent the combustion air intake, or properly size the gas, or make sure the water quality is appropriate. Also everyone wants to always use a Navien which I find to be more “sensitive” than some other brands regarding water quality. To each his own, I don’t recommend them for everything but they certainly have their place.


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## Tommy plumber (Feb 19, 2010)

Too bad you didn't install a tank-type water heater....


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## dhal22 (Jul 30, 2010)

We install both with no regards to the customers preference. I prefer the tankless that I've had in my house for the last 10 years but some still want tank only.


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## KCPlumb (Oct 26, 2021)

dhal22 said:


> We install both with no regards to the customers preference. I prefer the tankless that I've had in my house for the last 10 years but some still want tank only.


What Mfg/model did you install in your own home?


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## skoronesa (Oct 27, 2015)

KCPlumb said:


> What Mfg/model did you install in your own home?


Yes.


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## dhal22 (Jul 30, 2010)

KCPlumb said:


> What Mfg/model did you install in your own home?



I got about 8 years out of my awesome Eternal tankless before lack of support and o rings caused me to remove it and install a Navien a couple of years ago. Nothing wrong with Navien but it does not produce like the eternal did. 

We install enough Naviens that i keep 4 or so in stock at my shop.


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## Will (Jun 6, 2010)

I'd had really good luck with the Rheem RTGH-95DVLN-2 (made in Japan by Paloma). Tank mostly Bradford White since Rheem tanks went to crap (product quality and support)


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## skoronesa (Oct 27, 2015)

Will said:


> I'd had really good luck with the Rheem RTGH-95DVLN-2 (made in Japan by Paloma). Tank mostly Bradford White since Rheem tanks went to crap (product quality and support)


For tankless we install Rinnai, or Veismann. Overwhelmingly it's Veismann. Rinnai is for our budget customers. For electric, power vent, and atmospheric tanks we install State. Small indirects are those glass lined brown ones, can't recall the name. Large indirects we usually go with Phase III.


Nothing beats a Sepco though! Made from stone and steel, like the Rock of Gibraltar!


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