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Discussion Starter · #1 ·
Just noticed when up in attic today, havent noticed it before.

Even with the water off, the fan in the tankless heater keeps cycling on and off. Cycles on for 1 second, off for about 5, back on for 1, off for 5 and so on.

Its been doing this for about 1 hr all ready with the water off. Im guessing its not supposed to be doing this that long after the water has been off? Its a new unit about 4 years old, no history just moved in a few months ago. Its a Rinnai RL75. Thanks for any advice!
 

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Naildriver
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Although the water is off, the Rinnai is detecting a leak on the leeward side, such as a dishwasher, sink, tub, anywhere hot water can leak out. You are right, however, it should not be doing that. Turn the red and blue valves to the off position on the unit and see if it still cycles.
 

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The subject of a hot water recirculation system came up in another thread yesterday. That’s also something that could cause the water heater to run when there is no water usage, but the exhaust fan would not be running that often even then. The diagnostic codes available on the heater might provide some useful information. See page 36 of the manual.
https://www.rinnai-lms.com/resources/288/100000244(04) VC Manual.pdf

Chris
 

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Naildriver
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Good catch, @Chris616. The recirculator can act like a downstream usage, although it shouldn't come on all that often.
 
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