Atwood 8531-II Intermittent Burner Question( Photos Added)

[BFL13]

Furnace works properly starting and stopping with thermostat operation.

Problem is when on for a few minutes and warming the RV up, the burner quits and restarts after about a minute or less while the fan stays on. Once the RV is up to thermostat setting it shuts down properly.

Once in a while the burner will not come back on and the fan starts blowing cold air. Only way to fix that is turn the thermostat on /off wait for the fan to stop and then back on and it behaves until next time. This used to happen often, but is now rare. The problem now mostly is this intermittent thing.

What are the likely causes? Thanks.

[BFL13]

This will interest those with older RV's assuming the more common, later IV is something like the III. Doubt many on the forum will have the older II. Anyway---

I took out the II's board and replaced it with the III's. The III's is a little smaller in size, but the connections fit. No cover with the III's. I did not transfer the III's on/ off switch, not sure what that is even for.

Went camping again, furnace ran with no stumbles at all, very smooth. So I did not have to take it all out to get at that limit switch. Pure dumb luck!

[BFL13]

Thanks for that! I can see the limit switch on my spare III way in there so it looks like an all day job to get at it. 😞 I was hoping it was one of those things out front. Drat.

Looks like I have to take out the II from under the fridge. Might be easier to just swap in the whole III once the II is out anyway. At least, now I know what I am up against. Thanks again Doug and Old-Biscuit for sharing your knowledge.

The ducts all blow hot air strongly, so based on that it might be the board, I think the smart move would be to first just swap boards and see if that fixes it. If not THEN go after the limit switch. Maybe escape the chore of taking out the whole furnace.

[Old-Biscuit]

Left -----On/Off Circuit Breaker ----12V DC POS Red Wires

Mid...2 White Wires going into motor cover....Sail Switch, when it closes the DC from Sail Switch goes to High Temp Limit Switch and then to circuit bd via connector

Right...Timed Delay Relay. DC POS for on/off-cb goes to relay then to motor when relay is triggered by DC from T-stat



**High Temp Limit Switch is installed ON Heat Exchanger

[BFL13]

Thanks Doug, I will check that out.

Tried to find on google, but got confused. Here is my 8531-II and my spare 8531-III I got off a guy. He said it works (?) I have already stolen the burner off the III to use with my II.

The III has an on/off switch not on mine. Mine has a cover for the control board. What are the parts seen mounted going from left to right on these things? Not sure which is the hi-limit switch to swap. Be handy to know what the other things are too!

Thanks. My II first, then the spare III

[dougrainer]

1. Burner runs a few minutes cuts off then comes back on points to a hi limit switch
2. Inadequate hot air exhaust ducts or partially blocked ducts which will cause the Hi Limit to cut on and off.
3. If you replace the Hi limit and it still does it and duct work is open and no crushed ducts then the Main control module is bad. Doug