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Rinnai error codes 11 and 12 - crossflow issue?
We have a 4 year old Rinnai RL94 tankless water heater in our attic. Had been running fine since we purchased the house last November. Several months ago we began experiencing intermittent issues with getting no hot water. When I went to the attic to investigate the unit was flashing an 11 error code.
Since we are still (barely) under a home warranty program from purchasing the house, I figured I would let them deal with it. They sent out a plumber who said the unit would need to be descaled before he could do more troubleshooting. I had a second tech come out to do that. He told me that there's no way a scale issue could cause an error code 11 and he cleaned out the flame rods. Also assured me that gas supply (natural gas) appeared adequately sized.
He did however identify a separate water crossflow issue somewhere in the house (cold water entering hot water lines through a single handled faucet) and said I needed to have that issue fixed before he would do anything further. We have several single handled shower and tub valves throughout the house that could potentially cause such an issue.
I have identified the offending valve (thermostatic valve in a freestanding tub filler, of course there are no shutoff valves - I just replaced the cartridge and it still has crossflow issues - separate saga!)
My question is this - could a water crossflow issue possibly contribute to intermittent error code 11 (and most recently 12) issues? To me, the crossflow issue, from the heater's perspective, would manifest as reduced hot water demand from the heater - but unclear to me how this could cause 11 or 12 error code. My home warranty expires in 2 weeks and I really prefer to have them pay for any repairs, if the heater actually needs them - or do you agree with the tech that I could just be this crossflow issue?