Furnace gremlin

[Snappy347]

2021 Montana 3230CK
Dometic DFDM35

I live at approximately 6000 feet and visit in the winter in Buckeye, AZ, under 1000 feet.
I previously had trouble with the furnace cycling on and off at home for a couple of seasons. It won’t stay lit and continue to cycle until I shut it off. I replaced the regulator and sail switch last spring which didn’t seem to help. I finally tweaked the blade on the sail switch slightly (which I read about in another forum) and that helped a little here at home. When we went to AZ last fall it seemed to work fine except a couple of times. Now we’re home and it’s back to it’s old tricks of cycling. I’m looking for some in put as to what the problem might be. Could the gas pressure be effecting the performance? As I said, I have replaced the regulator but that doesn’t mean it is good.

 

[Daryles]

We had a similar issue while camping at higher elevation (Yellowstone Fishing Bridge 7,800') cold weather and low propane tanks. When we moved on to lower elevation and filled the propane tanks the problem corrected itself, or so we thought...
I discovered water intrusion on the furnace circuit board. I thought I had the cover sealed up pretty good. I put a strip of yellow Frog Painters tape (doesn't leave any residue) over the top edge to deflect rain away until I can reseal it properly.
You can see in the picture white residue of water intrusion.
Hasn't happened since I put the tape over the top edge. I also made a water defector cover for the exhaust.

 

[ChuckS]

In addition to possible water intrusion you might want to pull the burner section out and take a look see at its condition as well as the ignitor/flame sensor gap adjustment... many times the burner gets rusted up causing issues like what you are experiencing..

I camp twice a year at West yellowstone ( elev 6875 ) and have never experienced any issues in the last 12 seasons ( twice a year for 14 days at a time ) with the furnace....

You have an Atwood furnace and I have a Suburban furnace.. the nice thing is you have outside access panel to work on your furnace

 

[Bourbon County]

Your issue is very likely altitude related. You've probably heard the expression "the air is thinner"; the oxygen content in the air decreases at higher altitude. The oxygen is what's required for combustion. Your furnace has an induced draft type burner, the blower brings in outdoor air for combustion and exhausts the combustion gases. The air to fuel ratio is more critical in this type burner. The burners on your stove are like a propane torch; as long as it has some fuel and some air, it'll burn.

The standard gas pressure setting is between 11-13 inches in a water column which is based on an altitude of 2K feet, the new regulator likely came pre adjusted to that range. At higher altitudes you have to lower the gas pressure; the natural tendency is to increase, but that's wrong. When you lower the gas pressure, it will reduce the output of the furnace too. If you have a 40K BTU furnace, it'll be more like a 30K BTU depending on how much you have to reduce pressure.

There's a thread from September 2024 where a member was camping at 10K ft elevation in CA.
https://www.montanaowners.com/forums/showthread.php?t=91773

 

[ACKLM8]

As previously noted, the problem is likely due to altitude and reduced availability of oxygen, effectively making the combustion mixture too rich to burn properly. At 6,000 feet a significant portion of the earth's atmosphere is below you and while the percent of oxygen in the air remains relatively constant, the total amount of air is about 25% less than at sea level. I've been told that newer furnaces are better at accommodating these pressure changes, but that is just anecdotal. Not sure if there is a procedure for adjusting the propane flow to the burner, such as a smaller orifice. Would be interested to hear your outcome.

 

[Mikelff]

There are adjustable LP pressure regulators available on Amazon. You can adjust these for high altitude needs. If high altitude is your issue, and you camp in high altitude often, this might be worth trying.

 

[pjames32]

Ron…we can swap regulators. Mine works in Buckeye and at 6000ft

 

[Snappy347]

I’ve already replaced the regulator with a new one. That’s the first thing I tried.

 

[Snappy347]

I am up and running. Fingers crossed that it continues. A HVAC guy that is a member of our Elks Lodge campground suggested that I emery the tips on my igniter. He said build up will not let it sense heat well enough and can cause that trouble. I questioned that because of the age of the furnace but did it anyway and after reassembly it fired right up and has been working fine since. I also wanted to test the pressure from the gas valve but there is no possible way to get to the ports to hook up my manometer or adjust the diaphragm on my particular furnace. Poor design!