Attwood furnace intermittent issues

[rattle_snake1]

I have a 2003 truck camper with a attwood hydroflame (7920-II). Here in AZ it doesn't get much use, maybe once a year. It seems to run OK the 1st night and then fail the 2nd night. I seems to light on 1st ignition and heat for 5-10 seconds then shut off the gas valve. I looked once for LED blinks, didn't see any. It also has an intermittent squeal from the fan/blower.

At this time it wont fail. It works fine. Thinking maybe low voltage, I tested it down to 10.5 V and it still heats. All point thur the circuit have correct voltage. I didn't measure the gas regulator yet, but it will run heater + all stove burners fine.

I pulled the unit to inspect. There are no wear marks on the either of the blower wheels, or the sheet metal housing that would indicate interference. Not sure where the squealing is coming from other than the motor bearings. The motor spins smooth.

I pulled the burner and igniter. They look fine. The igniter gap was 0.150", it set to recomended 1/8 (0.125") There are no obstruction anywhere in the unit.

Not sure how the unit senses the flame. The igniter is the single wire type. Is the igniter also the thermocouple?

I re-installed the unit and everything works fine. Any help or thoughts appreciated.

[Jagtech]

The sail switch can cause this problem. They can start out being intermittent, then eventually fail altogether.

[3_tons]

Mine had the same intermittent squeal....Turned out to be the smaller blower wheel walking in and out on its shaft. A dab of glue did the trick...I also had the same issue with the burner repeatedly shutting down...Turned out to be the ignitor/electrode gap. A re-gap to 1/8" was the cure...

[ksg5000]

Intermittent squeal is likely from lack of use - some try lubricating fan bushing/bearing. I just turned the furnace on and let it run for an hour or so (cut off the propane so I wasn't wasting that) and I haven't heard the squeal again.

[Old-Biscuit]

YES the spark electrode is also the flame sensor. When main flame lights a milivolt signal is generated and goes back to circuit board to 'prove' main flame lit. Then circuit board keeps voltage on gas valve so it stays open until t-stat reaches set point and opens.

Clean it up, setting gap has probably cured your problems.
Just check grounds-clean tight
and pull connector on circuit board..clean contact surface with pencil eraser

Most problems are due to bad grounds and dirty contacts. Doesn't take much resistance to stop 12V DC