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Old 10-25-2020, 02:10 PM   #1
mattf
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M.O.C. #22665
Dometic Furnace Won't Stay Lit

Having problems with the furnace in our 2019 3021RL. When the furnace is turned on the unit kicks on with the fan running, burner then fires up, but burner immediately shuts off while the fan still runs. This sequence just repeats itself until I shut the furnace off at the thermostat. When the furnace is turned on I'm getting one flash from the red LED light, then nothing else from the light. The exhaust tube is clear, there's no moisture that would affect the circuit board, sail switch was removed and is clean and moving freely, propane tanks are full, batteries fully charged. Any thoughts on what to check next?
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Old 10-25-2020, 02:49 PM   #2
jsb5717
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If the furnace is actually igniting then everything before that in the pre-ignition sequence is fine, including the sail switch. The issue is likely with the igniter/sensor, manifold, or propane regulator.

Igniter/Flame Sensor - In many cases the igniter is also the flame sensor. If it is unable to read that the flame is lit then it will shut off the furnace. The flame sensor can either be faulty or not at the correct specified distance from the burner.

Manifold - This is the more expensive item to replace but if it isn't allowing the correct flow of propane it might be faulty.

Regulator - Your propane tank will typically be pressurized at 200 - 250 psi. The regulator will reduce that to a system operating pressure of 11 column inches of flow, which is approximately a 1/3 psi. If the regulator is not correctly adjusted or is faulty then the furnace ignition can fail to be sustained. It is possible to test the propane flow and adjust the regulator but that requires special equipment.

The easiest thing to check is the igniter/sensor for it's distance to the burner. You should be able to find that distance in the furnace documentation that came with your trailer. I saw in a video that it should be about 1/8". However, my docs say that mine should be more like 3/8". After that you might need to connect with a service tech to troubleshoot the rest.

My furnace is an Atwood, though I think many of the basic principles are the same for Suburban.

Here is a helpful video
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Old 10-25-2020, 04:38 PM   #3
mattf
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Problem resolved for some reason. I was only trying to turn on the furnace using the living room thermostat. When I turned on the bedroom thermostat as well as the living room the furnace lit after several attempts and now runs. Have no idea why, but it’s now working.
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Old 10-25-2020, 05:59 PM   #4
jsb5717
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I'm afraid one has nothing to do with the other. You're bedroom thermostat has no control over the furnace as it will only control the bedroom AC and heat pump (if it has one). I've had the same issue with mine in that it would start and stop just you described. I went through some of the troubleshooting as well and mine would stay lit after a few failed attempts. Now it seems to work as it should...can't explain why.

I was tempted to buy the parts to make my own propane pressure tester. I still may if the issue returns.
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Old 10-31-2020, 09:09 PM   #5
Renegade1LI
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Just had the same problem, I removed & cleaned the power wires to the board,hit the rest the code cleared & has been working since. If I had to guess the red 12ga wire on the front of the board was the problem.
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Old 11-01-2020, 05:44 AM   #6
RMcNeal
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Mattf, it may be as simple as some air in the gas line feeding the furnace. If you can, try lighting the stove first and bleed any air out of the lines, that usually will help.
Also, there could be spider webs or other debris in the furnace that finally burned up and got cleared to allow it to start working well. Been there, done that, got the T-shirt.
Just a few guesses for you to consider.
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Old 11-11-2020, 10:59 AM   #7
Twopetes
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Just wanted to add something that we had happen and just something to keep in your pocket. Our furnace acted similar. It turned out that the main LP regulator was bad and it was not allowing enough gas pressure when we lit the furnace. If there was a few minutes of nothing running before the thermostat called for the furnace, the gas pressure would build up enough for the furnace to fire, but there would not be enough pressure and flow to keep it running. Our local repair shop took a couple days but they found it. Regulators don’t last forever. I had to replace the regulator on the other LP tank and both pig-tails on our 15 HC. Always check for leaks! Good Luck!
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