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Rinnai tankless intermittent/off and on while not in use

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Have a Rinnai tankless water heater that was set at 120 and ran great for several years.

Recently, the additional control panel display with priority turns on and off intermittently. Happens while no taps are open and the in use LED remains off. When the panel turns off, the temp display disappears and the On/Off button is nonresponsive. When it turns back on, the temperature is reset to 104.

The panel generally only stays on for a few seconds before shutting off for a few seconds, often staying off for a minute or so. Every five minutes or so it will stay on for about a minute and I can raise the temperature to 120 before it turns off and comes back as 104.

Water from the tap follows the same behavior as the control panel display. Mostly groundwater cold, occasional mild temp, a rare 30 seconds of hot nirvana before the blizzard returns with scant promise of another distant patch of sun.

I noticed the hot water fluctuate more over the course of a few showers. This did not prepare me for the frozen hellscape of my next attempt.

This behavior began not too long after a power outage.

No codes display.

Is it normal for the control panel display to go out when tankless heaters shut off? Is it normal for tankless heaters to shut off while not in use? Any ideas on where to start?

I'm thinking to try cleaning the squirrel cage vent, flushing the system, checking the exhaust/intakes and condensation drain.

Maybe the recent power outage borked the board?

The unit is located in a tiny dirty terrible awful crawlspace so trying to go in with a plan. Cheers!

Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 2,806
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    It is maintaining a minimal temperature . Warms up the standing water . Keeps the unit dry for the long standby times

    There was an error rendering this rich post.

  • coldshowergobrr
    coldshowergobrr Member Posts: 3
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    Update

    Unit's actually outside as it happens lmao. It's an RL94. Turns out it isn't on the circuit labeled WH in the box. Nice! Turned off power at the unit for 10 min and once turned back on it stayed on long enough I could access the code history. Code 11 is the only code: no ignition.

    With the pressure relief open flame is visible but I can smell gas. Same results when I turned it on again after a good bit off and was able to get hot water from a faucet. Guessing there's incomplete combustion.

    Tried removing flame rod/igniter assembly and sanding the rods. No change.

    Next step seems to be blowing out the burners and burner box with 120 psi air; will try tomorrow.
  • 109A_5
    109A_5 Member Posts: 1,387
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    Hello, @coldshowergobrr,

    With a manual I found here;
    https://www.questargas.com/ForEmployees/qgcOperationsTraining/Water Heaters/Rinnai_RL75eRL94eR98LSeR98LSe.pdf

    104 Degrees F seem to be a default after an off period.


    I would verify the 120 Volt power to the unit is good and stable when the unit tries to work.
    The power outage or restoration may have damaged something or age related fading of the internal power supply is driving the digital logic stuff nuts, hence the erratic behavior.



    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    coldshowergobrr
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,110
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    Sounds like a bad sensor or Control board glitch 🤔 Mad Dog 
    coldshowergobrr
  • coldshowergobrr
    coldshowergobrr Member Posts: 3
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    Update

    Verified stable 120V at the incoming AC connector on the board while unit shutting off erratically. Seems like a bad board is the only culprit at this point. Ordering a replacement board
  • 109A_5
    109A_5 Member Posts: 1,387
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    Hello @coldshowergobrr,

    Another thing that could be done with the power disconnected is re-seat all the power connectors to the circuit board and make sure the pin fitment is secure. Loose connections cause problems.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System