Dometic furnace DFMD0121

MrWonderful · 07-27-2022, 11:10 AM

Hello All,

We have a 2021 Keystone Bullet 290BHS with Dometic DFMD0121 furnace. The furnace blower runs for a bit then cycles off. I don't hear any attempt at lighting, have run the stove to check for air pockets in the propane line, and have been told to check the sail switch. I removed everything to pull it out but it seems stuck. Is it siliconed to the wall? Do I need to remove the exterior exhaust bezel to try to scrape it free? I don't want it down for two months at the dealer waiting for the repair mid season.

thanks!

Bustinbeards · 07-28-2022, 04:53 AM

Sounds like you need to check and probably replace the sail switch

ChuckS · 07-28-2022, 05:06 AM

Look around the edges if the outer case for any screws that you might have overlooked that hold the furnace in place ..

No need to remove the outer duct .. it’s a tight fit and if you’ve been in areas with high humidity and salt air you may have a bit of corrosion to fight to get the furnace exhaust port to slide out of the wall vent tube..

Rocking it back and forth while pulling should break it free..

Since blower motor runs but you hear no ignition popping sound outside at exhaust and no LP smell most likely culprit is sail switch on an Atwood furnace ..

They are world famous lately for a cheap sail switch

MrWonderful · 07-28-2022, 05:59 AM

Thanks! I tried pulling, rocking, within reason worried about damaging the heater, but it didn't budge at all. The front, closest to me, lifts, but the back doesn't move and no additional hardware is present. I heard there maybe a lip on the front and the exhaust is super tight, thus exhaust port needing to come off for that extra movement. But I don't know.

No salt or lots of dirt, bought new, had for two seasons in southern Alberta.

Thanks for your responses.

jsb5717 · 07-28-2022, 07:29 AM

Can you reach back with a phone to try to take pics around the part of the furnace you can't see? A borescope could also help you see what's holding it up.

Also, is the propane line disconnected?

**sourdough** · 07-28-2022, 08:29 AM

If you haven't removed the exterior exhaust and it's the only thing on the exterior wall from the furnace you probably should give that a try. I've had one (a year old) that was stuck so tight in that tube that I almost had to bend it up trying to get it off. Rocking and twisting finally got it to break loose. That will be hard to do trying to use the furnace to twist. I'm sure if it that tight it would feel like it was stuck.

Bustinbeards · 07-28-2022, 09:17 AM

Is is screwed down to the floor at the base of the furnace?

MrWonderful · 07-31-2022, 12:10 PM

Had to remove the outside exhaust port to get access. So it’s firing now, but only burns for a few seconds then stops. Blower continues, but I can’t get a continuous burn. Thoughts?

MrWonderful · 07-31-2022, 12:45 PM

Had to remove the outside exhaust port to get access. So it’s firing now after replacing the sail switch, but only burns for a few seconds then stops. Blower continues, but I can’t get a continuous burn. I’ve run the stove for a while to clear any air. Thoughts?

MrWonderful · 07-31-2022, 02:16 PM

Tried running the stove and all that for airlocks. Almost like the propane stops, can’t smell it after it stops. Tried disconnecting propane as well.

Alpine Custom Upgrade · 07-31-2022, 02:36 PM

Quote:

Originally Posted by MrWonderful

Hello All,

We have a 2021 Keystone Bullet 290BHS with Dometic DFMD0121 furnace. The furnace blower runs for a bit then cycles off. I don't hear any attempt at lighting, have run the stove to check for air pockets in the propane line, and have been told to check the sail switch. I removed everything to pull it out but it seems stuck. Is it siliconed to the wall? Do I need to remove the exterior exhaust bezel to try to scrape it free? I don't want it down for two months at the dealer waiting for the repair mid season.

thanks!

Not sure if your furnace is like a central gas furnace in a house but there may possibly be a "flame sensor" rod that needs to be cleaned with a steel wool pad. It would connect by wire to the main board if so.
On a house unit, if the flame sensor goes bad then the fan stays on but no gas and no ignition. Have you removed power from it and returned power? (turn the breaker off and back on)(reset the board)? Just a thought and trying to help.

MrWonderful · 07-31-2022, 03:21 PM

Thx I will!

**chuckster57** · 07-31-2022, 03:23 PM

When you put the furnace back in, did you make sure the two exhaust ports lined up?

MrWonderful · 07-31-2022, 03:55 PM

Yup, it’s going out.

**chuckster57** · 07-31-2022, 04:01 PM

What I mean is both tubes are inserted into the furnace tubes?

92xj · 08-11-2022, 07:40 AM

This might help in your adventure

https://www.keystoneforums.com/forums/showthread.php?t=51049

Augie · 08-15-2022, 10:03 AM

Quote:

Originally Posted by MrWonderful

Had to remove the outside exhaust port to get access. So it’s firing now, but only burns for a few seconds then stops. Blower continues, but I can’t get a continuous burn. Thoughts?

I had the same problem exactly on mine. Had a mobile tech come out and he diagnosed it immediately as the burner orifice being misaligned. He said more common than you would think especially on new trailers. Took him less than 10 minutes and has run flawlessly ever since. By the way the mobile tech I used is in Okotoks. Let me know if you would like his info.

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