I have a problem with the Atwood furnace on my 5th wheel (2019 Montana High Country )I just bought the unit second-hand six months old from a private seller and have never used the furnace system before. (The person I bought it from never used the furnace either because they had free electricity at the RV park). When I turn up the thermostat and go outside, the furnace blower turns on, and the sparker clicks to ignite gas. I smell pretty strong gas exiting the exhaust pipe and actually hear the flame briefly ignite for ½ second or so, and feel a brief rush of hot air. Then the flame goes out. The sparker attempts to re-ignite, I feel a rush of heat for a ½ second, and then the flame goes out. This happens repeatedly over and over again until the unit finally times out and the red LED has the 3-blink pattern. Things I've tried:1) All the other propane appliances work. Stove works fine, gas water heater (which is right beside the furnace) also works perfectly. 2) Propane tanks are full. Any ideas of what I should try next would be much appreciated!Thank you!Randy

Sounds like the flame sensor is not detecting the flame although I would expect it to stay lit longer than 1/2 second. Could be a bad sensor or bad/corroded connection. It could also be the control board.I would also inspect for any obstructions / nests / varmints in the burner/exhaust assembly.

The control board on your furnace tries three times to prove a flame and then goes into a lock-out mode. You'll have to reset the thermostat to recycle it. It's working correctly.Mud-dubbers and spiders like to build their nests inside the furnace and block the proper flow of things. The screens you can get at RV supply stores do a great job keeping out the wasps but do nothing for the spiders. You'll need to open up the furnace and make sure there's nothing blocking the flame tube. There's flame rod where the spark jumps from and it must be surround by the flame rod to keep the gas valve open.

Thanks. The blower runs constantly for several minutes, with the sparker attempting to light every few seconds through that time period. It's like the flame just flickers in there before going out every time. I feel a burst of heat and that hollow "whooshing" sound that happens when the flame ignites, only for it to immediately go out. Only after several minutes does my unit go into lockout mode. I'll clean all the connections today and report back.

You need to pull the furnace and inspect the burner, LP orifice and igniter. I suspect you have a bug in the LP orifice or a mud dauber nest in the burner area. This is a common problem.

My furnace used to do that until I tightened all the push on spade connectors.

Atwood Furnace Problems | Good Sam Community

dougrainer
Nomad
Oct 20, 2019
IF under warranty, I would ask that the furnace be replaced. RUST is NOT a problem on Furnaces where you had rust. On a 2019, that is NOT right at all. Doug
cbr46
Explorer
Nov 12, 2019
I have a similar problem. My furnace is 17 yrs old. Some surface rust but overall pretty clean.

Fan comes on, a minute or so later gas is turned on and I can hear the igniter.
I can faintly smell propane coming out the furnace exhaust. Faintly. It comes & goes.
Sometimes the furnace will light but then goes out. I can hear a 'woof' or two . . . or multiples.
Sometimes it will run for a few minutes but never reaches a good outlet temp. Maybe 90F. It should be 120F+.

There were muddobber nests inside the flame chamber. They were cleaned out. Otherwise the inside was pretty clean.

The burner was removed and although it looked pretty clean I ran a quick wire brush on it (by hand). I also inserted a rubber coated wire into the gas jet. It went in easily telling me the jet wasn't clogged. I didn't remove the jet for more inspection.

Q1 - Control board, gas valve or rust inside the supply tube (clogging the gas jet)? #1 I don't want to spend $90 for a board I may not need and # 2 it's not exactly easy to disassemble (the supply tube nut is so tight I disassemble the fan shroud to get it out).

Q2 - Can I apply 12V to the gas valve to actuate it? For testing ONLY!

Thanks,
- bob
pushtoy_2
Explorer
Nov 14, 2019
my MH did that the circuit board got wet.. the vents on the out side were facing the wrong way and letting water in
marc71
Explorer
Nov 19, 2019
So I’m having the same problem as the OP was having... I have replaced the circuit board, sail switch and igniter... I also replaced the gas regulator, nothing to do with the heat issue just didn’t like the one that was on there. It’s an Atwood 8535. I took the screen part out where the gas flowes through, there was some rust blocking a few places, wire brush cleared that up. I put everything back together and still having the same problem... fan comes on, igniter lights and the heat blows briefly and kicks off, repeats two more times and shuts down, light blinking 3 times. I don’t know what else it could be??
cbr46
Explorer
Nov 19, 2019
I had muddobber babies INSIDE the gas suppy tube. How they got through the gas jet I don't know but they were clogging the jet.

I also had a pretty good mess inside the combustion chamber.

Good luck,
- bob
DFord
Explorer
Nov 20, 2019
cbr46 wrote:
I had muddobber babies INSIDE the gas suppy tube. How they got through the gas jet I don't know but they were clogging the jet.
Like you, I don't know how they're able to get inside there but it happens pretty often. The screens will keep the adults from getting in there to build nests and lay eggs. Spiders love to build a web across the hole in the orifice too.

It sure looks like they were awful busy bringing all that mud in. Cleaning it up is no fun.

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