Dometic furnance DEMD30111

[ThisIsMyUserName]

I installed this furnace in an older RV 12 months ago as the original Atwood furnace is no longer in production. This was dometics direct replacement.

The furnace ran great up until a few days ago, and it was only used during the very short Cali winter.

What it’s doing,
Starting up, fan working, it fires, and stays lit from anywhere from 1 second to several minutes doing this several times over. It eventually turns off and then repeats this process. It is giving no indication of fault via the circuit boards lights so I’ve been left to my own devices as to figuring this out.

What I’ve done/checked
-vents are not restricted and have good air flow
-I replaced the regulator even though I didn’t think that was the problem as all other appliances worked great. Strong blue flames.
-The propane tanks are full and new. And I’ve tried several.
-the sail switch was a little dusty, it got cleaned and I tested continuity.
-the burner was cleaned with a torch and a wire brush
- the spacing on the igniter is still at factory spacing and I do not know specifically what it is. I did take it off when cleaning the burner, was very careful with it so as not to bend it, and put it back on.
-power is good on batteries.

TheRV hasn’t moved in 3 years and has been parked in the same spot under a tent carport with sides and 5 foot clearance from wall. I believe the potential for moisture to have damaged circuit board to be very unlikely but always possible.

Any ideas?

Thank you,

-Cold Electrician

[jimcol]

Some have reported that the black resetting fuse in the DC distribution panel have caused intermittent problems. If you have such a beast might replace it with a regular blue fuse.

[Daryles]

The 2019 models had a bad batch of circuit boards. One of our members proved it by putting it in the freezer for a few hours, then testing it. It would not run. I don't recall the exact symptoms it exhibited.
He then put a hair dryer blowing on the circuit board to warm it up and it started working normally.
We had the symptoms you are currently experiencing while in Yellowstone Fishing Bridge (elevation 7,800'), it was very cold and that propane tank was low. When its first turned on, it would short cycle and turn off. I had to pull the fuse to restart the furnace (same thing as pushing the reset button on the outside). After many short cycles, the on cycle got longer and longer until it ran normally.
I'm guessing it warmed up enough to run.
The local RV Tech (yes they actually had an RV Repair station there at Fishing Bridge Yellowstone) I spoke to said that morning he had three other RVs doing the exact same thing. He believed it was a combination of low propane, very low temperatures and high elevation.
After we left Yellowstone the furnace worked fine (lower elevation, warmer weather and full propane tanks).
Just last week we had the same thing happen here at home. Outside temperatures at 0⁰F. It has not been above freezing in two weeks. The furnace would short cycle. I put heaters in the basement to warm up the air down there. The furnace has worked fine since then.

[mpkahl@att.net]

I had the same issue and just replaced the main board bought through amazon for $58. Lesson learned is if you have the face of it off and the vent tube removed it will not light and stay lit until you put the vent to back in with the cover off while you are touble shooting it Very important to have the vent tube in or it will light then go off and try it for 3 times and shut off.