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Rinnai RU199i Cycles On/Off then code 12

I have a Rinnai tankless water heater that is about 3.5 years old. It's recently started intermittently throwing a code 12. The failure seems to occur only when showering or occasionally when the kitchen sink is running. I can fill the bathtub and the unit works just fine. I've also tested and found that if I open 2 hot water taps while running the shower, the hot water supply is fine.
I viewed the performance data while running just the shower and it showed a flow rate of 1.1 gal/min which seems to indicate the flow sensor is working ok(?). While just the shower is running the unit's "In Use" light comes on, then cycles off, the flame goes out and the ventilation system kicks on. Then, the light comes on again and the process repeats. Cycles about 3 times before throwing the code.
It sounds to me like maybe this is an issue that only occurs when a moderate amount of water is flowing and the flame is modulating - am I thinking about that correctly? I cleaned the flame rod and igniter and have flushed the heat exchanger. Any ideas what other steps I should take to try fixing this?

Thanks!

Comments

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hello, As a start, let's make sure the problem is actually with the heater and not out in the plumbing someplace. So, try this test for crossover. Shut off cold supply to the heater. Open a hot tap. Does water stop flowing after just a few seconds? If not, there is a crossover and cold is leaking into the hot side, reducing flow through your heater and causing, or contributing to the problem. Let us know what you find. Thanks.

    Yours, Larry
  • nsuiter
    nsuiter Member Posts: 4
    I knew I was going to forget to mention something - I did a crossover test using those steps a couple days ago and after a few seconds the water does stop flowing so I don't think I have a crossover.

    Thanks!
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,785
    Hi, Here's a rundown of possible problems: https://www.home-water-heater.com/how-to-fix-rinnai-error-code-12.html#:~:text=An error code 12 found on the Rinnai,same error code appears on the remote controller. I don't have hands-on experience with this heater, but maybe others here do.

    Yours, Larry
  • Slimpickins
    Slimpickins Member Posts: 327
    A code 12 is a lost flame fault code. It sounds like you have a venting issue. Make sure venting is correct and unit not sucking in exhaust gases. I don't think you have a gas press issue since it seems to do it with a lower flow rate, its something to check though.
  • nsuiter
    nsuiter Member Posts: 4
    Took a couple videos of the burner in operation. One where the flame fails and one where it stays lit:

    Failure: https://youtu.be/Vq7slCC4w38
    Success: https://youtu.be/cbU698GUCuc

    not sure if that will help shed any light but thought it might be helpful. I’ll try checking and cleaning up the ventilation soon to see if that fixes it. Thinking I may need to clean the burner also.
  • Slimpickins
    Slimpickins Member Posts: 327
    Why don't you post some pics of the venting and termination. The last thing you want to do is clean the burners. It's a big job if you haven't done it before and you need gaskets and o-rings on hand.
  • mattmia2
    mattmia2 Member Posts: 7,202
    Is this one that has a magnetic flow sensor that can get fouled with magnetic particles in the water? Make sure there aren't any strainers in the inlet that are clogged too.
  • nsuiter
    nsuiter Member Posts: 4
    edited September 2022

    Here’s some pics of the air intake and termination. I can feel airflow from the exhaust termination when the unit is in use and can feel it pulling air when I open the unit up and put my hand near the opening of the noise filter (air intake).

    I think the flow sensor on this has a little pinwheel (not sure if it has any magnetic properties). I have cleaned the inlet filter and back-flushed the unit to try to clear any potential obstruction to the flow sensor. It does “feel” like a flow sensor issue since the flame almost immediately cuts off after igniting when there’s low/medium demand.

    This is the flow sensor part: https://wwcsupply.com/rinnai-107000269-water-flow-sensor-assembly.html


  • mattmia2
    mattmia2 Member Posts: 7,202
    Sometimes the flow sensor is a magnetic wheel that something like a hall effect sensor outside of the housing senses it rotating and because it is magnetic the wheel can get fouled with ferrous debris in the water.
  • Slimpickins
    Slimpickins Member Posts: 327
    It's not a flow sensor problem, it's either a combustion issue. 12 = flame failure. I see you're using room air, is the unit in room with a dryer?
    Have you called Rinnai tech support? If not call them and have a digital manometer, multimeter and your hand tools. 
     
  • JustWantHotWater
    JustWantHotWater Member Posts: 1
    First post here. I know this is a really old post. I am not a Rinnai technician. I am just an owner.

    What is the heater set to?

    I have "heard" that if it is set to 140, the min flow rate for activation moves from 0.4 GPM to 1 GPM as a way for the tankless to protect itself.

    You referenced how with the shower it is 1.1 GPM. I wonder if you are hovering around that min flow rate of 1.0 GPM and ultimately the tankless gets confused.

    Set the unit to 120 and see what happens.