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 Alternating Hot cold with tankless water heater
Author: Lloyd_90 (CA)

Hi everyone,

Thanks for reading. I've got a good one for those experts out there. I have a Rinnai tankless installed for a casita. It's not used much since it was built 2 years ago, so not sure when this started. There are two faucets and a shower. No matter which fixture I use for mixed hot and cold water, it cycles repeatedly between putting out warm water and ice cold water. Miserable when trying to shower! What I found out is that you can stop the intermittent cold water if I let hot water only run out of one of the other fixtures. What's the problem here?

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 Re: Alternating Hot cold with tankless water heater
Author: packy (MA)

does you model have a digital readout?
are you getting an error code?

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 Re: Alternating Hot cold with tankless water heater
Author: Lloyd_90 (CA)

Thanks for replying. No readout, it's an outdoor model:
Rinnai
V65EN 6.6 GPM Outdoor Low NOx Tankless Natural Gas Water Heater

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 Re: Alternating Hot cold with tankless water heater
Author: packy (MA)

having a digital readout makes life easy for a service tech or a homeowner to get some insight into what is going wrong.
after that it is experience..
i have not experienced that problem so i am lost..
maybe a call to rinnai tech support is in order..

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 Re: Alternating Hot cold with tankless water heater
Author: Lloyd_90 (CA)

That's actually a simple great suggestion. I'm hoping it's just the pressure regulator that needs replacement.
Thank you.

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 Re: Alternating Hot cold with tankless water heater
Author: Stoopalini (TX)

Tankless hot water heaters use a flow switch to turn on and off. Older units needed as much as 1gpm or more to turn on, while some of the newer units only need as low as 0.25gpm to turn on.

My guess is your flow switch has either gone bad, or there's mineral build up inside causing it to malfunction. I say this because you said if you turn multiple hot water faucets on, the heater will not cycle. Turning multiple faucets on increases the flow through the heater.

It is recommended to flush a tankless heater about once a year, with vinegar (or some other solution) to remove any build up.

There are plenty of videos on YouTube showing how to do this, as well as lots of articles online. A quick google search for "how to flush a tankless hot water heater" will get you good results.

Here's an example: [www.wikihow.com]

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 Thank you... Your advice is greatly appreciated!! :cheers:
Author: Lloyd_90 (CA)

Thank you kindly for this information! I will review this with the plumber who is coming next week.
Your advice is greatly appreciated!!

Lloyd



Edited 2 times.

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