2017 Bighorn Furnace Problem

[dkarl]

We purchased a 2017 3875FB in December and the furnace has never worked properly since bringing it home. We have taken it back to the dealership but still doesn't work properly.
It will cycle on and off for approximately 3 hours (which is great), then it tries to ignite again and after 3 failed tries it goes into lockout. You must then turn the thermostat off...wait at least a couple of minutes...then turn it back on and you are good to go for another 3-4 hours. Unfortunately, this usually means coming home to a cold RV and also having to get up at least twice during the night and wait around long enough to turn it back on.
We have tried 4 different propane tanks and that didn't fix it. The technician said there was a loose wire but that didn't fix it either. There is nothing blocking the return vent on the stairs. I am beyond frustrated as I really don't want to take it back to the dealership which is 1 1/2 hours away. Thoughts or suggestions are greatly appreciated.

 

[danemayer]

Hi dkarl,

The furnace goes into safety lockout mode, where the thermostat has to be reset, after 3 failed ignition attempts. This indicates that there's a lot working ok. For example, your blower, airflow, return air and sail switch are probably ok. If they weren't, rather than a lockout, ignition would not be attempted.

So the focus is on ignition and on flame sense. If ignition fails or if the flame sense doesn't detect a flame, you'll go into lockout after 3 attempts.

So the tech should be focused on 1) propane supply and gas valve, 2) igniter, 3) flame sensor.

Based on past reports, my guess is you have a bad control board. It opens the gas valve, supplies the power to the igniter, and gets signal from the flame sensor. Failure of the board is much more common than failure of the gas valve or igniter or sensor. And since the tech has already checked wiring, I'd assume it's not a wiring problem.

With an intermittent problem, positive diagnosis is difficult. I would suggest to the tech that a reasonable next step would be to replace the board, even if he can't demonstrate a failure.

I've attached a sheet that has additional specific info.