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Rinnai cycles by itself

Mykle Member Posts: 1

I wonder if I can ask the advice of anyone with Rinnai tankless heater experience. I installed an RC80HP heater three years ago and it's been very reliable. However, there are times of the day when it cycles on and off again all by itself, when no hot water is running anywhere in the house. When it does this it's on just for a second or less, but it'll do it several times a minute.

I imagine this is due to expansion and contraction on the hot side ... but I have a pressure-compensating air bladder installed on the hot side, which is supposed to prevent that being a problem (I thought). Maybe it's not at the right pressure, or something? Any ideas would be much appreciated.




  • Jack
    Jack Member Posts: 1,047
    The first time I saw this

    I thought there were ghosts. It was in a catering business. Having secured all faucets, bibs etc myself every few minutes the unit would pre-purge, fire and shut down immediately. After throwing the bones, offering a blood sacrifice and doing doe see does on one foot I realized that there was no check or back-flow preventer on the building water supply. Occasionally the flow in the street main was great enough to pull a negative pressure on the lateral feeding the building. Once the pressure in the main became neutral the water would surge back into the building causing the water heater to do its thing.
  • Slimpickins
    Slimpickins Member Posts: 340
    Exp tank

    I would move the exp tank to the cold inlet side and that should solve the problem. You don't really need an expansion tank unless you are heating a storage tank or using a small tank for recirc.or if your local code requires one.