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Troubleshooting SF-42Q No Heat, Fan Is Blowing

D

divinIN

Active member
Hello Everyone,

I have a 2021 390MP and am battling frequent furnace issues. We are in very cold temps and my son, daughter-in-law, and grandson live in it.

I have used online help and the steps received after contacting Alliance for help.

Summary Issue: Furnace blows cold, blower is working but not lighting

Troubleshooting so far and steps performed:
  1. Tested voltage at both sides of sail switch and both sides of service switch - good.
  2. Also tried testing voltage to ignitor (?) - the brown wire coming from the connector on the controller board that splits into two for both ignitors. I don't think I got a good connection on this, but tech I spoke with at Alliance said 99% of the time it is the board, not the ignitor.
  3. Removed furnace and took to a local RV shop. Bench test revealed faulty controller board.
  4. New controller board installed.
  5. Installed furnace and switched to a full propane tank.
  6. Furnace lit after three or so attempts and was running for about a week. Last night it stopped igniting again. My son tried cycling the furnace about seven times, no luck.
Today I am going to check the voltage again at each point and will report back the results.

Any further suggestions would be most appreciated. I had to buy an electric heater to help keep the rig warm.

Thank you in advance.
 
D

divinIN

Active member
I checked the voltages again today and everything looks good. I am having a hard time getting to the ignitor wire so I'll try again tomorrow. What I did notice today is the little wizard button must have been pressed on the converter. I pressed it, the lights immediately got brighter, and the LED light pattern changed to the normal setting (had to look up what normal was). After that I tried two more times and the furnace finally started again. Maybe coincidence, not sure. I will keep updates coming as I make, or don't make, progress.
 
D

divinIN

Active member
Update on this. My son and I created our own bench test kit with a 12V battery and a portable propane tank. Everything that I knew to check checked out. So I took the furnace into a local RV shop and the issue is one of the two gas valve solenoids - it isn't opening when sent the signal from the board.

I will post pictures and more info on the specific part when I get the furnace back, which is hopefully today. I have to say I'm a little perturbed I couldn't find the issue myself because I really don't like paying for something I could have done myself. But...there's always next time.
 
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