Dometic furnace woes

[toolittletime]

I have a new 2019 Carbon 417 Toy hauler. The furnace problem started virtually the first week that we were full timing. Here's what it does.

Blower comes on for about 10 seconds and then you can hear the furnace ignite and puts out heat exactly like it's supposed to. This last for 4-5 days, then no heat.
After that, blower comes on and runs for 45 seconds or so and then shuts off.
I called a local service man and he has been out 4 times...only charged me 1 service call fee. He replaced the limit switch last time....was going to replace the sail switch, but apparently everyone is out of stock.
Funny.....everytime he comes out and disconnects the furnace to work on it, it works for a few days....then kaput.

It is a Dometic model DFMD 35121
I have the troubleshooting guide, and have researched all of the repair techniques here and on youtube...question is where to go next, should I pull it out and check all connections??.......replace the sail switch when one is available??? order a new circuit board off amazon??

Thoughts....Suggestions??

One other thing....I have already replaced the 12cf Nevercold fridge....it worked for one week...replaced it with a residential model. Norcold sent a brand new replacement a few weeks later that I am selling.
Wiring.......gas lines etc do not scare me, but I am tired of paying for repairs that last only a few days.
We are full timers, so there is no chance we will be dropping the unit off at a shop......although I may pull out the heater and take it in for repairs under warranty.
We are currently near Austin TX.
Tim

[sourdough]

Others will chime in with different ideas but I'm thinking control board. If it works for days just fine, drops off the charts and starts cycling the fan, you disconnect it and it works fine again for a few days - that sounds like a control board to me. Had a very similar issue and to get through a cold spell I went out and disconnected the power lead, let it reset?, reconnected it and I was good to go for a bit. New control board fixed it.

[chuckster57]

I’m leaning towards a board too. If you get a repair under warranty, Dometic will require OEM board. If you pay, buy a dinosaur brand.

[LHaven]

In my new rig, my sail switch was fouled by sawdust and leftover styro chips. Is it possible yours is also fouled, and the impacts involved in servicing the heater knock off just enough fouling to make it operate until the crud blows back onto it?

If you have spare time, maybe you could try a no-cost cure of removing the sail switch, cleaning it, and taking a vacuum to the cavity. Might work.

[Aireman]

Dang! I have the same model with the same problem and have a repairman coming Wednesday. Hope they have the parts.

[toolittletime]

Thanks for all the comments gang.
The parts are out of stock everywhere online, and my repair guy is still waiting on one from Dometic....they are also out of stock.

From all the comments I think I'll go ahead and order the dinosaur board, and pull the heater out.....check the operation of the sail switch....check all connections etc. Last time it worked for 4 days before crapping out....frustrating!!!!

It will be a few days before I have time to do the repair, as I am working on my new RV pole barn here in Texas....will post back my results when finished with repairs.

Tim

[toolittletime]

Which Dinosaur board for the Dometic DFMD 35121 furnace....anyone know??
Tim

[JRTJH]

Which Dinosaur board for the Dometic DFMD 35121 furnace....anyone know??
Tim

Give Dinosaur Electronics a call at (541) 994-4344. They are open 8-5 Monday through Friday Pacific time. Have your furnace model and serial number handy and they will tell you exactly what you need to order.

[toolittletime]

Thank you John!!

[Roscommon48]

how about talking to dometic...they may help.


if it is a 2019 I would assume it is under warranty...push for warranty coverage reimbursement from keystone.

[toolittletime]

Thanks all....
I called Dinosaur as suggested and they recommended the Fan 50 plus board available on Amazon for 91.00. I pulled the heater and installed the board and it has been working perfectly (fingers crossed) for the past week. The board was a little bit of a pain since the corner mounting lugs had to be removed carefully without breaking the corner off the board. While I had it out I tested the sail switch.....it was working properly.

The biggest pita was having to crawl in the belly and disconnect everything, and then pull the heater through a hole I had cut in the bottom of the pantry. Other option was to remove and reinstall the water heater......not!!! Sucks having to cut a hole in a new trailer, but I put everything back in with screws, so the next time I have to access it,and I'm sure I will, I will not be cussing as much.

Tim

[jlonginav]

I’ve been battling the same issue. Control board and thermostat were replaced in Late Feb. Two days ago it stopped igniting again. On tank was empty so I got it filled and reset everything. Last night it stopped igniting again. All my efforts to reset failed. These include turn the breaker off and removing power from control board. The light on the ignition board was on then off for three seconds. Manual states a Limit / Airflow error. Last troubleshooting step was to remove and inspect sail switch. I saw nothing on the switch and no debris blocking airflow. After re-install of sail switch all has been functioning. I have ordered two just in case. Would you RV experts recommend I replace the limit switch as well?

The is a Atwood-Dometic AFMD 35131. Installed on 2018 Keystone Cougar 367FLS 5th wheel

[LHaven]

For what it's worth, I'm on my third Dometic furnace failure in a 2019 rig, and I determined that the furnace comes with a two-year warranty, the second year of which is covered by Dometic. Your dealer may or may not be an approved Dometic warranty center; luckily, mine is. As of last Wednesday, my rig is back in again to get the furnace repaired under warranty.

I know a lot of you people are skilled enough to do these jobs yourself and get them done right, but on the other hand, maybe if Dometic has to eat enough warranty labor, especially in the second year when they don't have Keystone to cover it, they will learn how to make a reliable heating system.

[jlonginav]

Thanks, as soon as I can it is headed for a service shop. I do have an extended warranty

[chuckster57]

For what it's worth, I'm on my third Dometic furnace failure in a 2019 rig, and I determined that the furnace comes with a two-year warranty, the second year of which is covered by Dometic. Your dealer may or may not be an approved Dometic warranty center; luckily, mine is. As of last Wednesday, my rig is back in again to get the furnace repaired under warranty.

I know a lot of you people are skilled enough to do these jobs yourself and get them done right, but on the other hand, maybe if Dometic has to eat enough warranty labor, especially in the second year when they don't have Keystone to cover it, they will learn how to make a reliable heating system.


Dometic pays the warranty labor, during the first year Keystone is the warranty “administrator”, and acts as the middleman. After the first year the dealer will deal directly with Dometic. In the end Keystone doesn’t pay, the appliance manufacturer does.

[jlonginav]

I’ve been battling the same issue. Control board and thermostat were replaced in Late Feb. Two days ago it stopped igniting again. On tank was empty so I got it filled and reset everything. Last night it stopped igniting again. All my efforts to reset failed. These include turn the breaker off and removing power from control board. The light on the ignition board was on then off for three seconds. Manual states a Limit / Airflow error. Last troubleshooting step was to remove and inspect sail switch. I saw nothing on the switch and no debris blocking airflow. After re-install of sail switch all has been functioning. I have ordered two just in case. Would you RV experts recommend I replace the limit switch as well?

The is a Atwood-Dometic AFMD 35131. Installed on 2018 Keystone Cougar 367FLS 5th wheel
Just a update. About 4 hrs running good. Now we have some decent rating and thunderstorms. I’m now getting the ignition lockout error. Fires up 3 times but won’t stay on.

[toolittletime]

I’ve been battling the same issue. Control board and thermostat were replaced in Late Feb. Two days ago it stopped igniting again. On tank was empty so I got it filled and reset everything. Last night it stopped igniting again. All my efforts to reset failed. These include turn the breaker off and removing power from control board. The light on the ignition board was on then off for three seconds. Manual states a Limit / Airflow error. Last troubleshooting step was to remove and inspect sail switch. I saw nothing on the switch and no debris blocking airflow. After re-install of sail switch all has been functioning. I have ordered two just in case. Would you RV experts recommend I replace the limit switch as well?

The is a Atwood-Dometic AFMD 35131. Installed on 2018 Keystone Cougar 367FLS 5th wheel

Did you replace the control board with the same as original, or the Dinosaur brand?

[jlonginav]

It was replaced at a service center so I suspect an original

[chuckster57]

If Dometic paid a warranty claim, OEM is required.

[toolittletime]

That could be the problem......just sayin !

[sourdough]

In my lifetime I've had 3 furnace control boards replaced; one a week ago on a new HC. They were all under warranty and OE. I've not had one fail after replacement but who knows; maybe the replacement OE boards are Dinosaur boards rebadged? ...:lol::lol: I will say I have to take this one out and put it through its paces for several days since I've not been able to.

[Fuzion1278]

OK, add me to the list of Keystone, (2018 Fuzion Toy Hauler), campers who's Dometic unit works for a day or so then locks out after trial for ignition. Same mechanic two different times said the sail switch "hangs up' periodically and will not make. He said he thinks it's because our unit is mounted "on its side". This is an approved mounting position according to Dometic. I have an extended warranty through a Jayco dealer so it's going back to a local Jayco dealer with the instructions that I don't want it back until it's fixed. I am going to try to push them to install a pressure differential switch instead of this cheap sail switch. They probably will not because it is not an approved repair but I am in the HVAC business and I know the pressure differential switch will be a much better air proving device than a cheap sail switch. I would do it myself but as one member noted, getting to this unit is through the underbelly, removing every air hose, gas fitting, electrical fitting, over water lines while lying on your belly. I just do not have time for this! :banghead:



Others thoughts?