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Plumbing in the Home/Rennai tankless water heater


Hello,  water heater is almost 5 years old.  It has begun to stop producing hot water during time when 2 or 3 showers are in use but it sometimes cuts off with only 1 shower in use.  Temp goes from full hot to ice cold immediately.  Wait ten minutes and it usuall comes back to hot.
Volume and pressure seem to remain normal.
Installer says its a valve problem.  Plumber says he cant find a valve problem.  I ran my own amature diagnosis..all three showers on working OK, then I turned on on faucet on the upstairs bathroom sink for hot water, all water went immediately cold.
Any suggestions?  Thank you.

Hello, since those tankless heaters work on flow, meaning they have to sense flow to come on

I have to agree with the installer. It sounds like the burner is kicking out due to either a flow switch issue or a flame sensor issue or it could possibly be a gas valve problem. I would have the installer or a qualified plumber come and test all the  controls. Your problem is intermittent. You could try contacting Rennai or one of there reps.

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Jay Nicholas


Plumbing & Heating (warm air, hot water & steam heat)


40 years in the business, 40 years as a lic. master plumber in NY State. Retired

Graduated Magna cum laude at the School of Hard Knocks

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Commercial, residential and light industrial. You name it ...I have probably worked on it

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