Rinnai - Cold Water Sandwich when recirc is on

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cTogar

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Hi - we have a Rinnai Tankless, RUR98i, installed as part of a new build. It has the recirculation feature, which we have been told should give us instant hot water and avoid a cold water sandwich.

Since we've moved in, we've experienced the following - When the recirc is on, we do get (nearly) instant hot water throughout the house. However, after 30-60 seconds, the water will get increasingly cooler for another 60 seconds. Then it will heat back up again to full heat.

We've been told that this cold water sandwich shouldn't happen with the recirculation on. The plumber, working under warranty, has been largely unhelpful. Any suggestions or similar experiences with this heater? Are our expectations correct?
 

WorthFlorida

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Does this install use a dedicated return line or a crossover? Don't go by timing only. Most new faucets uses only 1.25 gallons per minute so it can take a long time to push water to the faucet. Older faucets were 2.0 gallons per minute or higher flow rates.

Read page 39. It might answer your question. There maybe a balance of timer, low and high temperatures settings. I do not know much about these units other than what I read from manuals.
https://www.questargas.com/ForEmployees/qgcOperationsTraining/Water Heaters/Rinnai_RUR98i_RUR98e.pdf
 
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WorthFlorida

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Hello cTogar, I hope your problem has been fixed.

FYI... Here is a post found by another user that had a problem with a different brand and it fixed his problem of cool water after the initial hot water. It turned out the problem was a check valve I I think it was in the unit. He took it apart and reassembled and it is working. These two postswere for a Navien units and as you read it get quite complicated in the switch settings. It's why I asked if you have a dedicated return or use the cold water line with check valves.

https://terrylove.com/forums/index....-showers-check-valve-issue.88086/#post-654744
https://terrylove.com/forums/index....nternal-recirculating-mode.86848/#post-628548
 

cTogar

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[QUOTE="WorthFlorida"[/QUOTE]

Thanks WorthFlorida! We had someone else out yesterday, with no luck. They're going to try and connect with Rinnai directly, see if they can help. i'll take a look at these threads and pass them along. I'm honestly not sure if the return is dedicated or not.
 
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