I have a 2019 classic. Furnace blower comes on but but then shuts off - no heat. The water heater ignites and plenty of propane. I remember reading about a some kind of switch?? Where do I start?

Start with the thermostat. Clean the contacts on it, by taking off the cover and gently easing a piece of fine sandpaper between the contacts. I do this about every spring after the unit has been sitting over the winter. Sometimes, after a dusty journey, I clean the contacts.?

If the blower comes on its not the thermostat.?

But it could be a whole bunch of other things.? Some potential problems:

1. The sail switch, which senses that the blower is on, is defective
2. The battery is low so the blower doesn't blow hard enough
3. The exhaust outlet is blocked so the sail switch won't trigger
4. The igniter is bad or dirty and won't light the propane
5. The sensor that determines the propane is lit and hot fails.
6. The propane jet is clogged so the flame either won't light or burns too low.? If the jet is clogged you?
? ? ?probably need to blow out the propane lines too.? One person on this site replaced the whole furnace
? ? ?but the problem still didn't go away.? Clogged lines suck.
7. The controller board is bad.

For a DWYer you might get it fixed in a day, or might spend weeks ordering parts until you find the culprit.? Or you could take it to an RV place and they'll fix it in an hour or two, but that will cost some $$$.

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Cindy Harris
Pittsburgh, PA
2013 Expedition

If the blower comes on, but you don't hear a click within about a minute latter or you hear several clicks and no heat it is most likely the sail switch.? I had this same problem last year on my 2021 Classic. I ordered a new sail switch which is a different model number (apparently updated) and have not had a problem since.? If you are mechanically inclined you can DIY.

Bob, you had to take the furnace out to replace the sail switch, right?? How hard was that to do?

It requires a bit of work, disconnecting the gas line and exhaust pipe, etc. ? But the hardest part for me was getting the unit out from under the sink!

On Sun, Oct 29, 2023 at 12:08 PM, BobF wrote:

It requires a bit of work, disconnecting the gas line and exhaust pipe, etc. ? But the hardest part for me was getting the unit out from under the sink!

?Do you have to take the exhaust outlet off the side of thd trailer, or does the furnace just slide off of that?

Mine is under the sink too.

Yes, you might be able to pull out the unit from the exhaust pipe, but to reinstall it you will find it necessary to take the exhaust pipe off, install the unit, and then align the exhaust pipe so it fits over the heat exchanger pipe properly. Don't screw down the unit before doing this. The exhaust pipe then has to be resealed on the outside of the camper when it is reinstalled.

I have taken my furnace out and reinstalled without removing the exhaust.? It does take a bit of reaching into the cabinet and wiggling to get it aligned.

I had an issue with bee nest inside the pipe.? I caught it before it got to the sail switch.? But I think bees may be a big problem with interfering with the movement.??
I wonder if you could use a leaf blower to blow into the exhaust so any debris at the intake would blow out the intake.? But look into both intake and exhaust first to clean anything you can see.
The circuit board makes sure the sail switch opens AND closes to prove it is freely moving before allowing gas.

I placed a screen over the outside to keep bees out.? The purchased screen comes with some springs to clip it on.? I smeared a thin coat of clear silicone over the top surface of the screen, back to the wall and just slightly over the edges to create a rain/drip cap.? I don't often use the furnace as a cube heater on low in more than enough and typically have electric.

I took Steve’s advice to heart and decided I try a few easy things and then take it in if they didn’t work. I blew some compressed air into the exhaust. I hooked up the stove and ran it for a few minutes. Turned the furnace off and on. It worked. Not sure why…spider web, block in the line?? Anyway, back in business.

One word of caution for anyone who takes out the furnace is to look into the heat exchanger pipe to see if there is a metal disc with a hole in the center properly seated in the pipe.? When I looked at mine after removing the furnace, I noticed the disc lodged on its side in the pipe. After several emails to Dometic, I found out that the customer service reps were not technicians and did not know anything about this disc.? They would not give me any contact info for their technicians or engineers to inquire about this so I managed to remove the disc, slightly bent the tabs surrounding the disc and reinstalled it in the pipe, pushing it in with the exhaust pipe .

More furnace comments:

That list of 7 things i posted that could go wrong is incomplete.? There also is a furnace delay relay that can go bad, and a furnace overheat sensor that can go bad.

One youtube video said you should remove and service your furnace every other year, starting with year 1.? Why year 1?? To catch the mistakes made by the manufacturer.??

One guy had a lot of trouble getting the outside furnace vent cover and vent tube off a 3 year old trailer, because of rust, and mentioned that 3 years was a long time to wait for service.

Hmmm. I guess my never been serviced 12 year old furnace is about due.

If you get mud wasp nests inside your furnace you won't be able to blow those out with air.? Here in California I get mud wasp nests inside my garage, and sometimes they're so solid I can't break them up with my fingers.? But we have high quality mud here.

There aren't too many youtube videos on removing our small atwood furnaces.? Most of the videos show elbows and arms being shoved in the small furnace opening, and you can't see what they're actually doing.

They sell screens on Amazon that clip over the exhaust of the furnace and keep the bugs and bees from getting in.? But those reduce the airflow, and may prevent the sail switch from turning on the gas.? But after seeing the guy on youtube dump a half dozen mud wasp nests out of a furnace, maybe I'll get one for at least in the garage.

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