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Open Roads Forum  >  Tech Issues

 > Furnace Burner Keeps Cutting Off

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avarusbrightfyre

San Diego

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Posted: 11/10/20 07:33pm Link  |  Quote  |  Print  |  Notify Moderator

Hello all,

So I'm having an issue where the burner for my Dometic DFMD 30111 furnace keeps cutting off while it's trying to heat my travel trailer. It does still heat the trailer, but the burner cuts out, then comes back on, then cuts out again, then comes back on. It will eventually get over whatever the issue is and stay on until it reaches temperature, but it goes through this issue every time the furnace turns back on. The blower fan stays on the whole time and there's no error light from the control board when the burner goes out or comes back on.

The following are the things I've checked or considered so far:

- During my first winter, I learned that one of the wire connectors to my sail switch is a bit loose and I figured out how to get it to stay in contact, so that was my first thought, but that doesn't appear to be the problem. I just checked it for dirt/debris and it's totally clean...and last time the error light came on when that connector was the problem but I'm not getting any error lights now and the burner does cut on normally.

- The furnace is mounted vertically in a very open compartment under my entertainment center and I can't find a specific return air vent in my travel trailer for what most people would have as an open air return. The manual says it gets return air from the openings in the case (which are many), and I didn't have this issue last year, so I don't believe it is a return air flow problem.

- I just had to replace my propane regulator for the second time, but a windex leak test doesn't produce any bubbles, and the problem started before I replaced it, so I don't think that is the issue.

- One of my searches indicated that a bad thermostat could be a problem, but the unit does heat normally aside from the burner cutting off prematurely. As stated before, the unit eventually stays on until the heat cycle is complete, so I'm not sure it's a thermostat problem unless there's some other consideration with those that I'm not aware of.

I'm not really sure where to look next. Internet searches bring up the issues I've listed above, but I'm suspecting it's some sort of internal problem that requires disassembly of the unit. I'd hate to pull the whole thing out and take it apart only to find out it was something stupid I didn't know about and disassembly wasn't necessary.

Has anyone else had issues like this and found a simple solution? Or is it likely a clogged burner or some other internal problem and I have to take the whole thing apart?


2019 34' Minnie Plus Travel Trailer
San Diego, CA


Old-Biscuit

Verde Valley

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Joined: 06/20/2009

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Posted: 11/10/20 10:47pm Link  |  Quote  |  Print  |  Notify Moderator

This was posted in another RV forum by 'A1RVTraveler'

I am a mobile RV tech and I am going to suggest something you need to try.

The 2017-2019 Dometic Atwood furnace has been experiencing some problems with sail switches not staying closed during furnace operation. This has been especially problematic with furnaces mounted vertically.

A new sail switch was introduced that has cured the problem.

This is how I troubleshoot.

Removed the sail switch and bracket from the furnace. Leave all wires connected.

Have someone turn on the furnace.

Once the motor starts, close the sail switch with your hand and keep it closed.

If the furnace ignites and runs fine, the sail switch needs to be replaced with the new style switch.

You can not close the sail switch until the motor starts.

Let me know what happens.

Matt

PS:

The new sail switch comes with a modified bracket to allow the sail switch to travel an extra 1/32". Seems odd, but this cures the problem. The actual sail switch in not bad, just not staying closed during operation.

This only applies to 2017-2019 Dometic-Atwood furnaces with straight blade sail switches, not the angle bent sail switches.


See post #28


Is it time for your medication or mine?


2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
On the Road Debt Free April '07
Off the road still Debt Free Jan. '14

wolfe10

Texas

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Posted: 11/11/20 06:11am Link  |  Quote  |  Print  |  Notify Moderator

Old-Biscuit wrote:

This was posted in another RV forum by 'A1RVTraveler'

I am a mobile RV tech and I am going to suggest something you need to try.

The 2017-2019 Dometic Atwood furnace has been experiencing some problems with sail switches not staying closed during furnace operation. This has been especially problematic with furnaces mounted vertically.

A new sail switch was introduced that has cured the problem.

This is how I troubleshoot.

Removed the sail switch and bracket from the furnace. Leave all wires connected.

Have someone turn on the furnace.

Once the motor starts, close the sail switch with your hand and keep it closed.

If the furnace ignites and runs fine, the sail switch needs to be replaced with the new style switch.

You can not close the sail switch until the motor starts.

Let me know what happens.

Matt

PS:

The new sail switch comes with a modified bracket to allow the sail switch to travel an extra 1/32". Seems odd, but this cures the problem. The actual sail switch in not bad, just not staying closed during operation.

This only applies to 2017-2019 Dometic-Atwood furnaces with straight blade sail switches, not the angle bent sail switches.


See post #28


Not sure I go along with this one as first thing to check. Could the sail switch be faulty-- certainly.

But, remember what it does for a living-- it VERIFIES proper air flow for before allowing the furnace to ignite.

So, start by verifying that the air return to the furnace is not blocked, all ducts in good condition (not crushed) and all vents open. Also a good idea to check from the outside for dirt, mud dubbers nests, etc before firing it up for the first time of the season.

If all the above are good, connections to the PC board good and clean (or use DeOxit to clean the connections) THEN suspect the sail switch.


Brett Wolfe
Ex: 2003 Alpine 38'FDDS
Ex: 1997 Safari 35'
Ex: 1993 Foretravel U240

Diesel RV Club:http://www.dieselrvclub.org/

Old-Biscuit

Verde Valley

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Joined: 06/20/2009

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Posted: 11/11/20 08:51am Link  |  Quote  |  Print  |  Notify Moderator

wolfe10 wrote:

Old-Biscuit wrote:

This was posted in another RV forum by 'A1RVTraveler'

I am a mobile RV tech and I am going to suggest something you need to try.

The 2017-2019 Dometic Atwood furnace has been experiencing some problems with sail switches not staying closed during furnace operation. This has been especially problematic with furnaces mounted vertically.

A new sail switch was introduced that has cured the problem.

This is how I troubleshoot.

Removed the sail switch and bracket from the furnace. Leave all wires connected.

Have someone turn on the furnace.

Once the motor starts, close the sail switch with your hand and keep it closed.

If the furnace ignites and runs fine, the sail switch needs to be replaced with the new style switch.

You can not close the sail switch until the motor starts.

Let me know what happens.

Matt

PS:

The new sail switch comes with a modified bracket to allow the sail switch to travel an extra 1/32". Seems odd, but this cures the problem. The actual sail switch in not bad, just not staying closed during operation.

This only applies to 2017-2019 Dometic-Atwood furnaces with straight blade sail switches, not the angle bent sail switches.


See post #28


Not sure I go along with this one as first thing to check. Could the sail switch be faulty-- certainly.

But, remember what it does for a living-- it VERIFIES proper air flow for before allowing the furnace to ignite.

So, start by verifying that the air return to the furnace is not blocked, all ducts in good condition (not crushed) and all vents open. Also a good idea to check from the outside for dirt, mud dubbers nests, etc before firing it up for the first time of the season.

If all the above are good, connections to the PC board good and clean (or use DeOxit to clean the connections) THEN suspect the sail switch.


The issue is the Straight Blade paddle sail switch 'flutters' causing micro switch to open/close...which drops DC and then passes DC so circuit board drops DC to gas/valve then energizes gas valve...flame on/off/on/off

Bent paddle sail switch has slightly move upward movement which holds micro switch CLOSED...no 'fluttering'

Simple check of which style paddle...straight or bent and voila ---issue IDd

avarusbrightfyre

San Diego

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Joined: 01/05/2020

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Posted: 11/12/20 11:01pm Link  |  Quote  |  Print  |  Notify Moderator

I finally got around to testing the sail switch as described above. I took the sail switch out of the housing and held it closed after the fan came on and I'm still experiencing the problem. Still not getting the air flow error light from the control board, either.

JaxDad

Greater Toronto Area

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Joined: 08/02/2011

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Good Sam RV Club Member

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Posted: 11/13/20 05:58am Link  |  Quote  |  Print  |  Notify Moderator

If the blower bushings are dry fan speed will drop but not necessarily enough to throw a code.

If that happens you could hit the high temperature limit causing the burner to do exactly what you describe.

Try putting a little oil, the proper stuff, there’s a difference, I like 3 in 1 electric motor formula (which comes with a nifty extension tube too BTW).

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