Furnace Problem

[Coug60]

New Montana owner here. 2019 3121RL. So, I took my 2019 Montana out for elk season and my furnace went psycho on me. My furnace is a Dometic. That’s what’s on the Thermostat
Situation:
1. Turn furnace on at Kitchen thermostat
2. Fan starts
3. Burner kicks on 2 sec kicks off 5-10 seconds
4. Burner kicks on 5 sec kicks off 5-10 seconds
5. Burner kicks on 2 sec kicks off 5-10 seconds
6. Burner kicks on 10 sec kicks off 5-10 seconds
7. Burner kicks on 25-30 sec kicks off 5-10 seconds
8. Fan never stops, and furnace never shuts down until I turn it off.

#3 thru #7 happen in no particular order and times you can vary 5 to 15 seconds... seldom the longer.

I have two thermostats, one in the bedroom and one in the kitchen area. None of them are located next to a vent. I’ve been using the kitchen thermostat so turned the system off and then tried using the bedroom thermostat just to see what would happen. Bedroom thermostat although is powered will not activate the furnace.

Any ideas?

[AZ Traveler]

Shannon,

The files section of the forum includes a furnace troubleshooting guide. Common problems include: sail switch, airflow restricted by wasp nest & bad regulator.

[jsb5717]

Welcome aboard! Sorry for your furnace issues...but you're not alone. Furnace problems are pretty common.

The fact the furnace is igniting eliminates a few troubleshooting steps. We know it's not a sail switch or igniter.

First thing to check is whether or not you have an auto-reset fuse (black). I doubt it's that at this point since the fan keeps running. But if you do, I'd still replace it with a standard 15A fuse (blue).

With your symptoms the usual suspects are:

• Air flow, as Zack said. Check to make sure that there's no bug nest impeding flow.
• Hi Limit Switch - If it's tripping prematurely then it will kill the burn. They rarely go bad but are pretty easy to bypass with a jump wire to test.
• Burner/Diffuser - This is located on the burner assembly, mounted to the propane valve. It requires that you disconnect the propane line from the furnace and pull out that assembly. The burner (or diffuser) is very simple. All it does is evenly disperse propane for a clean burn. If it is rusted over so that holes are plugged, or burned through with larger holes, then your symptoms is the result. Once it's out it's very easy to replace if needed.
• Propane Regulator. The furnace has a high demand for propane flow. An RV regulator is preset at 11" column inches of flow. The furnace needs all of that to properly run. If regulator output diminishes your other appliances can still run normally, but the furnace can falter. The first time our furnace failed it turned out to be the regulator. If your rig came with a Fairview regulator then that could easily be the culprit. If you need to replace it get a Marshall Excelsior.
• Propane valve (in the burner assembly). Not as likely but they can fail. I ended up replacing one on my buddy's furnace. Don't start with this one.
• Main Control Board - Not as likely but always a possibility. Since it controls all functions there are several ways they can fail

Troubleshooting these things can be tricky without all of the proper equipment. That often results in starting to just replace parts...which is a bummer but may be unavoidable. Do the easy things first that don't cost anything. I now have a backup part for every replaceable component on our furnace. After having it fail 3 times I just decided to have the parts handy so I don't get stuck in the cold away from home.

Good luck with the project and please keep us up to date on progress to see if there's more insight to get you up and running.

[MandK]

I also experienced a furnace issue last winter, I did the trouble shooting with the help of this forum and some YouTube videos. Turned out it was the igniter. Mine would light sometimes and not other times. Once it lit, it stayed lit until the thermostat called for it to stop. But in my research, iirc, I found out that the ignitor is also a flame sensor. If the flame goes out, it shuts the gas off. So I guess that if it is not sensing the flame right after it lights, that could be another possibility. Good luck with it and keep us informed in case it’s something we haven’t heard of before.

[Coug60]

Thanks for the info Jeff... I used to me in maintenance when I was in the USAF. . Electro/mechanical. With that Im going to go with easiest/cheapest fixes first so,


1st. Propane Valve- easy and cheap. Little voice is telling me this is it but...

2nd. Burner/Diffuser- easy don't know what they cost

[Coug60]

Thanks for the info Mark, Its in the rotation for possible fixes.

[jsb5717]

Originally Posted by Coug60

Thanks for the info Jeff... I used to me in maintenance when I was in the USAF. . Electro/mechanical. With that Im going to go with easiest/cheapest fixes first so,


1st. Propane Valve- easy and cheap. Little voice is telling me this is it but...

2nd. Burner/Diffuser- easy don't know what they cost

Do you mean propane regulator? That's more likely. It's located by the propane tanks. There is also a propane valve (located in the furnace). It's a possibility but would be farther down my list. The only way we figured out it was the propane valve (not the regulator) on my buddies furnace is that I had my backup valve which happened to be the same one on his furnace as well.

We pulled out his, applied 12v power to it, which opened it up like it would in operation, and we applied air from a simple inflator (used for swim floaties). We had nothing to measure the output. But we did the same thing with the new valve and the air flow was significantly stronger. So we installed the new one and his problem was solved. A little MacGyver, I know, but it worked.

The burner is easy to check without spending any money. If it's clean just put it back and check it off the list. If it's rusted up then replace it and try the furnace again.

[Daryles]

We had a similar problem in June.
Elevation was the issue.

https://www.montanaowners.com/forums...rnace+limiting

Just curious, how cold was it?
For your model year (and mine 2019) there was a bad batch of control boards that would not work properly at freezing temperatures. One of our members troubleshoot and identified the problem by putting the boards in the freezer for a couple of hours then tested it. It didn't work. He put a hair dryer on it to warm it up and it started working. He went through several brand new boards that had the exact same issue.

BTW, the bedroom thermostat only runs the bedroom AC unit. However the thermostats are identical and can be swapped for troubleshooting.

[Coug60]

Originally Posted by jsb5717

Do you mean propane regulator? That's more likely. It's located by the propane tanks. There is also a propane valve (located in the furnace). It's a possibility but would be farther down my list. The only way we figured out it was the propane valve (not the regulator) on my buddies furnace is that I had my backup valve which happened to be the same one on his furnace as well.

We pulled out his, applied 12v power to it, which opened it up like it would in operation, and we applied air from a simple inflator (used for swim floaties). We had nothing to measure the output. But we did the same thing with the new valve and the air flow was significantly stronger. So we installed the new one and his problem was solved. A little MacGyver, I know, but it worked.

The burner is easy to check without spending any money. If it's clean just put it back and check it off the list. If it's rusted up then replace it and try the furnace again.

So being mechanically/electronically inclined but a novice on furnaces I watched some videos to get a grip on the nomenclature.
So even though my burners are lighting I checked everything that is possible without having to remove the furnace. Luckily for me I have access to it from the outside.


1. Ive jumper'd the limit switch, no change in problem
2. I pulled the Sail Switch out looked at it and tested good reinstalled, no change in problem
3. I pulled the burner out (like new) put back in, no change in problem
3A. Checked electrode. I have a 1/8th in gap and its not to far from the burner. Dont know what the distance from the burner is suppose to be. its about a 1/4in away from the burner at most.


I have ordered from Amazon one of every item that's easy to access and replace so just to have on hand in the future if Im out in the back country.
A new Propane regulator arrives today and a new control board on Saturday.
I will be stumped if the regulator or control board doesn't fix the problem.
I purchased a extended warenty so will fall back on that to fix it. Its a pain to take it into the city and deal with the rat race at the shop.
I think the furnacw has been pulled before as it does n ot have the original sealant around it.

[Coug60]

Originally Posted by Daryles

We had a similar problem in June.
Elevation was the issue.

https://www.montanaowners.com/forums...rnace+limiting

Just curious, how cold was it?
For your model year (and mine 2019) there was a bad batch of control boards that would not work properly at freezing temperatures. One of our members troubleshoot and identified the problem by putting the boards in the freezer for a couple of hours then tested it. It didn't work. He put a hair dryer on it to warm it up and it started working. He went through several brand new boards that had the exact same issue.

BTW, the bedroom thermostat only runs the bedroom AC unit. However the thermostats are identical and can be swapped for troubleshooting.

It was in the low teens... Its at home now and 60s durring the day. No change in problem.

[jsb5717]

Given the things you done and the symptoms you have I tend to agree that looking at the regulator or control board are logical steps.

Can you post a link to the regulator you ordered? Would like to confirm we're on the same page and talking the same language.

You'll be a furnace expert in no time. It's good that you've take such a hands-on approach to learn the various components. It's also worth your time to learn the fire-up sequence these things go through. For instance, the fact that your furnace is actually firing tells us that the sail switch and igniter are both doing their jobs.

Keep after it...you'll get it. But post that regulator to see what you got.

[Gonefishing]

Yep seems furnace problems are common. I’m having one now also. Mine is only when trying to use gas. Comes on and after 15-20 seconds cuts off. Everyone tells me it’s the sail switch. Bought new switch replaced it same thing. What I don’t understand if I remove the sail switch from the motor and hold it in my hand the sail will lay against the switch and furnace will run fine. My thought was the fan wasn’t pushing enough air to keep the sail against the switch when installed. Held my hand over the hole where the sail goes and the fan is pushing air a good 2 inches from the motor. So I would think that’s enough to close the sail against the switch. I finally gave up and have a tech coming out to check it out. I will post the results when it is fixed.

[jsb5717]

Originally Posted by Gonefishing

Yep seems furnace problems are common. I’m having one now also. Mine is only when trying to use gas. Comes on and after 15-20 seconds cuts off. Everyone tells me it’s the sail switch. Bought new switch replaced it same thing. What I don’t understand if I remove the sail switch from the motor and hold it in my hand the sail will lay against the switch and furnace will run fine. My thought was the fan wasn’t pushing enough air to keep the sail against the switch when installed. Held my hand over the hole where the sail goes and the fan is pushing air a good 2 inches from the motor. So I would think that’s enough to close the sail against the switch. I finally gave up and have a tech coming out to check it out. I will post the results when it is fixed.

I've learned that just about anything is possible. It's possible that there's something wrong with your fan so that there is reduced air flow. However, I'd be more inclined to look again at the sail switch. Does the new one look exactly like the old one? Does the old one work when pressed in your hand? I've seen new sail switches just not work very well. Did you buy an OEM or aftermarket switch? Did it have good ratings? Sometimes they can work when vertical but not horizontal. Sometimes the sail just needs a little tweak to better catch the air.

[Coug60]

Originally Posted by jsb5717

Given the things you done and the symptoms you have I tend to agree that looking at the regulator or control board are logical steps.

Can you post a link to the regulator you ordered? Would like to confirm we're on the same page and talking the same language.

You'll be a furnace expert in no time. It's good that you've take such a hands-on approach to learn the various components. It's also worth your time to learn the fire-up sequence these things go through. For instance, the fact that your furnace is actually firing tells us that the sail switch and igniter are both doing their jobs.

Keep after it...you'll get it. But post that regulator to see what you got.

Just swapped out the Propane Regulator, no change in problem so I have put the original back.
Next is the control board arives Saturday....

[Gonefishing]

Originally Posted by jsb5717

I've learned that just about anything is possible. It's possible that there's something wrong with your fan so that there is reduced air flow. However, I'd be more inclined to look again at the sail switch. Does the new one look exactly like the old one? Does the old one work when pressed in your hand? I've seen new sail switches just not work very well. Did you buy and OEM or aftermarket switch? Did it have good ratings? Sometimes they can work when vertical but not horizontal. Sometimes the sail just needs a little tweak to better catch the air.

I finally gave up and called a tech to check it out. Will know in a day or two,what the problem is.

[Coug60]

Originally Posted by Gonefishing

Yep seems furnace problems are common. I’m having one now also. Mine is only when trying to use gas. Comes on and after 15-20 seconds cuts off. Everyone tells me it’s the sail switch. Bought new switch replaced it same thing. What I don’t understand if I remove the sail switch from the motor and hold it in my hand the sail will lay against the switch and furnace will run fine. My thought was the fan wasn’t pushing enough air to keep the sail against the switch when installed. Held my hand over the hole where the sail goes and the fan is pushing air a good 2 inches from the motor. So I would think that’s enough to close the sail against the switch. I finally gave up and have a tech coming out to check it out. I will post the results when it is fixed.

Could also be a clogged/dirty air return or vent if the fan isnt getting enough mass to move it properly...
In any case my problem has elements of your so interested to find out what your fix is going to be...

[Coug60]

Well Ive checked everything that can mechanically shut down the burners...
The electrode looked fine but know whey to verify its integrity, everything else seem ok.
If the Bord doesn't work the only thing left before I call a tech is to pull the furnace (doesn't seem that it will be that hard, I have outside access) and check/blow out the returns and vents.

[Gonefishing]

Originally Posted by Coug60

Well Ive checked everything that can mechanically shut down the burners...
The electrode looked fine but know whey to verify its integrity, everything else seem ok.
If the Bord doesn't work the only thing left before I call a tech is to pull the furnace (doesn't seem that it will be that hard, I have outside access) and check/blow out the returns and vents.

I will post what the fix is for mine when it’s fixed

[rohrmann]

Originally Posted by Coug60

Well Ive checked everything that can mechanically shut down the burners...
The electrode looked fine but know whey to verify its integrity, everything else seem ok.
If the Bord doesn't work the only thing left before I call a tech is to pull the furnace (doesn't seem that it will be that hard, I have outside access) and check/blow out the returns and vents.

You've checked all the mechanical stuff, but have you checked the batteries? The motors in these furnaces draw high amperage, and maybe if the batteries are less than perfect, maybe the voltage drops off as the motor is running and it slows down and the sail switch opens, shutting down the furnace. This is just guessing, but might be worth checking.

[Coug60]

Originally Posted by rohrmann

You've checked all the mechanical stuff, but have you checked the batteries? The motors in these furnaces draw high amperage, and maybe if the batteries are less than perfect, maybe the voltage drops off as the motor is running and it slows down and the sail switch opens, shutting down the furnace. This is just guessing, but might be worth checking.

I have the Lithium Batteries, they are running great and well maintained. Not very old either