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Rinnai Water Heater Error Code 12

Hi, I have a Rinnai water heater (RUC80i) that worked fine for 5 years but trouble started right after the 5-year mark. It is 5 years and 6 months old now.
It flashes error code 12 when a faucet is open but works with the shower or when dumping water through the relief valve (Large water volume). It works only at max water temp and turns off when mixing water in the shower or when the temperature is set at less than 120 at the control panel. Previously it had error codes 10 and 11 and had the Water flow servo & sensor, flame rod, burner thermistor, fan, and igniter replaced. It gets flushed every year. The latest diagnosis is that the heat exchanger should be replaced, and Rinnai will cover the part but not the labor.
Is there something that the technicians may have missed? Is it worth fixing anymore? Thanks.


  • kcopp
    kcopp Member Posts: 4,386
    At this point I would cut my losses. Next I would figure out why this has been as issue. What is your water like? Is your basement on the damp side (could affect electronics). Is a tankless your best option? There are other ways to get hot water.
    Larry Weingarten
  • koko2842100
    koko2842100 Member Posts: 4
    My water comes from the city and is filtered through a whole house filter so no sediment passes through. My neighbors have no similar tankless issues. I am considering a conventional tank water heater.
  • kcopp
    kcopp Member Posts: 4,386
    I guess it would depend on the city then? how hard is it?
    Big difference from an east coast city vs a city in west. Scale and hardness are more of a problem out west. Tank type heaters do tend to have less issues.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,687
    Seems like a water flow problem . Tankless are sexy and has a place . But if you have the room a simple tank makes more sense .
    I have enough experience to know , that I dont know it all
  • koko2842100
    koko2842100 Member Posts: 4
    Hardness may not be a problem because the City water source is from treated surface water and ground water. Also this water heater is flushed every year.
  • Slimpickins
    Slimpickins Member Posts: 339
    edited March 2023
    More than likely you have dirty burners since you had a code 10 before, that means you have a restriction. Usually its not the heat exchanger. The burners can be removed to clean but it can be a big job if you've never done it before. It's easier to replace the burners just in case you find them bad (cracked) after you remove them plus it comes with gaskets, ignitor, flame rod and new solenoids and they aren't very expensive. Is your exhaust termination near a dryer vent?
  • koko2842100
    koko2842100 Member Posts: 4
    I decided to cut my losses and go for a new tankless. Thanks all for your comments.