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Rinnai Error Code 12 (ONLY WHEN COVER IS ON)

tjball2010 Member Posts: 2
edited March 2020 in Domestic Hot Water
Ok. We are in desperate need of some help. The run down...
We have an RU98i Rinnai tankless unit for PROPANE. We bought our house 8 months ago. We started getting an error code 12 pretty immediately when we just had 1 shower going. It wouldn't happen right away, but after a few minutes the unit would shut off and throw that code out. We had plumbers come out, the entire unit has been cleaned and the exhaust tank in the back of the unit was replaced (it had been cracked). Error code 12 persisted. It was determined that our gas line was too small and they upgraded to a higher size. Error code persisted. Rinnai told our plumbers that the flu was installed incorrectly as it was installed for a non-condensing unit, but ours is a condensing unit. Great, we replaced the flu with the correct parts. Rinnai also sent over a new burner because they figured they would have been compromised from incorrect installation. So now we have a new gas line, new flu, new exhaust tank, and new burners. We run the hot water in multiple baths and showers and it never kicks off. We believe the problem is solved. Plumber goes to put on the cover and the unit shuts off within 30 seconds. We pull the cover off, the unit works without a hitch. Put the cover back on, it shuts off within 30 seconds. K so something is happening to make the error code 12 throw ONLY WHEN THE COVER IS ON! Can someone help us? What can we do?! We feel so close to having this thing fixed, but can't figure this next step out. Thank you!


  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,753
    edited March 2020
    So, this unit has a concentric vent that draws air in the outer pipe and discharges flue gases through the inner pipe. Check to make sure there aren't any obstructions of the outer pipe at the terminal end because it sounds like the boiler is not getting enough combustion air.

    There's plenty of air coming through the front of the boiler with the cover off. When you replace the cover, the boiler relies on air being drawn in from the concentric vent.
    Often wrong, never in doubt.
  • tjball2010
    tjball2010 Member Posts: 2
    @Alan (California Radiant) Forbes ok so maybe you can help with this. We just pulled the flu apart and my husband thinks that it's possible the wrong connection is in the vent top kit. That is the only part that was not replaced. So the inside pipe on that vent top is metal, not the PVC. I can't find a picture of that part anywhere to see that the inside of it is PVC and not metal. Thanks again! Really appreciate the help.
  • OK - remove the vent termination and see if the boiler behaves.

    Take some pictures of the flue and its parts and post them here so we can see.
    Often wrong, never in doubt.
  • rick in Alaska
    rick in Alaska Member Posts: 1,178
    Error 12 is a flame loss. My first thought was the same as Alans, but I can not figure out how the cover comes in to play. The air intake and exhaust are both on the outside of the casing, so even if the termination is compromised, the cover should not matter if it is on or off. Rinnai has a boat load of wires inside of it, and I am wondering if the cover is pushing on some of those wires and maybe messing up a connection. Check all the connections.
    Also, check the flame rod and ignitor.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,129
    Hi, Long ago I had a Raypack heater doing the same thing. Called out the rep. It turned out to be a wire in the wrong place that would short when the cover was in place. I was embarrassed!

    Yours, Larry
  • BillyO
    BillyO Member Posts: 264
    possible cross contamination. Had similar problem with Laars mascot.
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