Atwood Furnace Isssue

[Cline88]

Carl n Susan,

I'm having a similar issue to this with my Montana 3711FL Atwood 8535 IV-DCLP furnace. I am getting a flame sense fault light code on the circuit board. It seems one thing after the other is going wrong with this unit. I have replaced circuit board, then it worked, then the blower motor started making noise and failed, that was replaced. While disassembled I replaced the burner head which was rusted through, the electrode was fine. It was cycling on and off normally for several days then suddenly it stopped cycling regularly. Hit the reset On blower and it worked again. Unit now fires up , I hear combustion and a few seconds later it cycles off and then tries to ignite again. Where should I start looking for my problem.

I cleaned the burner head area out as well when I had it apart found a few ladybugs hiding below the burner head when I removed it. I also feel like Im smelling a acrid smell from exhaust or something stronger than I remember in previous years ( I can not determine if it is propane Im smelling in the exhaust, or if I am just going crazy from frustration) . We are hooked to a large propane tank and everything else seems to be functioning well. I would like to note our propane is at 30% currently ,,,,would this cause a pressure issue? I feel like I have used it with less in the tank than that before. Any suggestions or tips would be greatly appreciated.
Thanks - Cline88




MOD Update: Post moved to a new Thread as the previous Thread was 8 years old and not applicable.

[Carl n Susan]

Not being proficient with an Atwood furnace, I can only suggest following the directions in the service manual (below)

If there is no sign of blockage in the burner tube (mud daubers, etc.) then it might be time to do some diagnosis work. Here is a link to an Atwood Furnace Service Manual to guide you on the steps

[jsb5717]

What year is the rig? If it's only a few years old then you might suspect the propane regulator. With a new control board it's not likely to be the culprit...but always possible so don't discount it outright. Also, have you checked your furnace fuse in the fuse panel? If it's black then it's the resettable type and they are prone to constant failure. They begin to trip prematurely and weaken more every time they trip. Best solution if you have that type is to just replace it with a standard blue 15a fuse. That may or may not solve your problem but replace a resettable fuse regardless.

The OEM Fairview regulators can start to fail. The other appliances can continue to run normally due to lower flow-rate demand but the higher flow-rate demand of the furnace can expose a failing regulator. The max set rate for RV regulators (11 column inches of water) is also the demand rate for the furnace. So if the regulator flow rate starts to diminish then the furnace can falter. It can start up with the available propane at ignition but quickly run out of adequate flow to sustain the burn. I am aware of 4 or 5 different instances where this was the issue.

Sadly most people don't have the test equipment to prove whether or not the regulator is failing so the cheapest way to find out is to just try it. Replacing the regulator with a Marshall Excelsior solved it for us. I see them regularly on eBay for around $40. if you get one DO NOT get the low flow version.

[Mikendebbie]

Info from their profile ‘about me”…2015 3711FL

[twindman]

Originally Posted by Mikendebbie

Info from their profile ‘about me”…2015 3711FL

MIkendebbie - good to know! I have been on here since 2006 and didn't know this! Thanks

[LeftOverParts]

We had a similar issue a couple weeks ago with furnace staying lit for 30-60s. Then it would go out and the circuit board would start clicking for about 3s and get one LED blinking. I used the chart form Daryles in post 7 (thanks) and found a partially kinked hose on the convenience center-side propane tank. Evidently, I didn’t clock it right when installing the tank after filling to avoid the kink. In researching this issue, I also found that the lines can get clogged with oil.

https://www.montanaowners.com/forums...ad.php?t=92084

[pitman44]

Flame sense is difficult to test on an RV furnace. One of two things is happening. First is that the board isn't sensing it properly which is a board replacement. The other is there's some resistance to the signal making it back to the board properly.

Start at the ignitor wire at the board. Make sure that connection is clean and tight. Crimp the female end slightly if it pulls off easily. If the wire comes off the ceramic ignitor, take it off and again make sure it's clean and tight. Measure the resistance thru the wire. Should be less than an ohm. Clean the ignitor. A dollar bill works well. Emory cloth isn't recommended, but I've used it in a pinch. With most furnaces the ignitor spark is to the burner. See what the gap is. Not sure what it's supposed to be on yours, but 1/8" is common. Take a wire brush, sandpaper and clean the area where the spark hits. Assuming the ignitor is sparking to the burner take the burn off and make sure where it connects to the furnace is very clean, free of dirt and rust. Hopefully there's a screw holding it to the furnace.

I should mention it could be the wire from the board to the ignitor or the ignitor has failed enough to be an issue. But making sure the ground path is excellent will often take care of the issue.

When the system makes a spark that's a few thousand volts so it's relatively easy to make the spark happen. With flame sense the board is measuring micro-amps DC. I don't know what value an RV furnace control board is looking for, but with residential gas furnaces it could be looking for as little as 1.5 micro-amps DC. Doesn't take much of a poor connection to be a problem. I hope this helps.

[Thudly]

I just went thru this, being hooked up to a large propane tank. Oil from the propane tank filled up the burner unit. I plased a trap directly after the regulator with a ball valve to drain the oil. Every couple days I open the valve and each time I am surprised how much has acumulated. From what I understand, home appliances burn hot enough where the oil is not a problem. Google oil in propane .