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Rinnai RUCS75 randomly stops heating water

My Rinnai (about 1 year old) will stop hearing water randomly even thought he faucet is on full hot and it originally turn the heater on and kept it hot for 2-4 minutes... turning water all the way off and back on will restart the heater and then 2-4 minutes turn cold again.

I am puzzled as this seems like a flow issue, but no errors are shown on the display window.

Secondly the heater will make a loud vibration/groan noise occasionally and I am not sure what would cause this... the problem are mutually exclusive.

Any guidance would be great



  • Larry Weingarten
    Larry Weingarten Member Posts: 3,247
    Hi @Digitalsoul4, For starters, have you contacted Rinnai? They should have a clue. o:) The loud noise/groan... do you have low water pressure? That could allow boiling to happen, particularly with bigger draws. Have you checked the inlet screen? Junk in that could cause your troubles.

    Please do let us know what you find.

    Yours, Larry
  • gerrytheoilman
    gerrytheoilman Member Posts: 8
    Is the rinnai running and heating water but the tap is cold? Check pipe at outlet of water heater, if its hot shut of cold water to rinnai if sink is still running you have a cross connection. I also agree with checking screen since you should be doing at the every year mark, you will be surprised sometimes at the buildup of sediment. Also the groan you speak of did install check the combustion? Is it propane and tank is low or pressure regulator checked? You could call for a service and make sure they do a combustion check.