2022 Furnace Question

[Paul & Deb]

I have searched but can't find a post with this issue.

I have a 2022 22MLE with a Surburban SF=25Q furnace. We've only stayed in this new trailer maybe 7 nights total and have used the furnace for short amounts of time to warm the trailer up in morning and at night but then shut it off and it always worked fine.

My grandson has been staying in the trailer (next to the house) for the past week. The furnace was turned on and working great with the temp set to about 68 during the day and then down to around 60 at night. Everything was working fine for days until the last couple days I would go in to find the furnace wasn't working. I could turn the temp up to 80 and it wouldn't do anything. I checked the fuse just in case and it was fine but as soon as I reseated the fuse, the furnace came on. It then worked for the day. The next day the same thing. I went to check it and nothing. As soon as I pulled and reseated the fuse it came back on.

The fuse never blows and once I reseat it, the furnace works as designed.

Any thoughts?

TIA

[Cate&Rob]

Hi Paul,

I am not very familiar with the Suburban furnace. Hopefully Howard howson will join this discussion.
Pulling the fuse is usually a complete "circuit board reset". Are there any indicator lights on the main panel after the furnace stops cycling normally?

Rob

[Paul & Deb]

Hi Paul,

I am not very familiar with the Suburban furnace. Hopefully Howard howson will join this discussion.
Pulling the fuse is usually a complete "circuit board reset". Are there any indicator lights on the main panel after the furnace stops cycling normally?

Rob

No indicator lights are lit but I would imagine that's because the fuse is intact. Of course, when I pull the fuse the red indicator light illuminates until I reseat the fuse. Your point that pulling the fuse is essentially resetting the circuit board may lead me to believe there is a bad circuit board.

[Cate&Rob]

Might not be the circuit board . . . but, it could be a sensor or timer that inputs information to the circuit board. Since the system worked correctly for a while, it is not likely a wiring or thermostat problem. I tagged Howard earlier (who has completed some training on these things). I am also going to tag Colan colan who may have some ideas on what is going on here and/or what to check.

Rob

[Country Campers]

Paul & Deb

Paul,

Here is a file that I have found, hopefully you will find some info in it. Just wondering what your battery voltage is, I realize you are probably connected to shore power but if the batteries are low this could be an issue.

Brian

Suburban-Furnace-Master-Service-and-Training-Manual.pdf

[howson]

Paul & Deb -- when you state "reseat the fuse" I assume it's the fuse in the thermostat?

I suspect the thermostat is bad--easy to check by tying together the two blue wires that *should* be there at the thermostat. If unsure of which wires post a pic of the back of the thermostat.

I'm sure you realize the thermostat is nothing but a switch. The blue wires are used to pass 12vDC to the control board (when the thermostat calls for heat) to start the blower (which subsequently leads to the next operation in the start-up sequence).

Without reseating the fuse, if shorting the two blue wires together does not start the blower...then the thermostat is likely OK.

From there I'd check to ensure there's 12v on both blue wires at the control board (with the thermostat calling for heat). If 12v is making it to control board via the blue wires (again, when the thermostat is calling for heat) but nothing is happening...other than the control board the only other thing I can think of that would cause no response from the furnace is a sail switch stuck closed...but that's not a common fault, and resetting the fuse on the thermostat wouldn't magically unstick the switch (so based on the symptoms the sail switch is an unlikely cause).

[Paul & Deb]

Paul & Deb

Paul,

Here is a file that I have found, hopefully you will find some info in it. Just wondering what your battery voltage is, I realize you are probably connected to shore power but if the batteries are low this could be an issue.

Brian

[ATTACH]n73197[/ATTACH]

The trailer is plugged in, and the batteries are at 100%

[Paul & Deb]

Paul & Deb -- when you state "reseat the fuse" I assume it's the fuse in the thermostat?

I suspect the thermostat is bad--easy to check by tying together the two blue wires that *should* be there at the thermostat. If unsure of which wires post a pic of the back of the thermostat.

I'm sure you realize the thermostat is nothing but a switch. The blue wires are used to pass 12vDC to the control board (when the thermostat calls for heat) to start the blower (which subsequently leads to the next operation in the start-up sequence).

Without reseating the fuse, if shorting the two blue wires together does not start the blower...then the thermostat is likely OK.

From there I'd check to ensure there's 12v on both blue wires at the control board (with the thermostat calling for heat). If 12v is making it to control board via the blue wires (again, when the thermostat is calling for heat) but nothing is happening...other than the control board the only other thing I can think of that would cause no response from the furnace is a sail switch stuck closed...but that's not a common fault, and resetting the fuse on the thermostat wouldn't magically unstick the switch (so based on the symptoms the sail switch is an unlikely cause).

Howard, I'm actually talking about the furnace fuse in the 12vdc panel. I haven't touched the thermostat at this point. If I remove that 15a fuse and put it back in the furnace restarts. Interestingly though, when I notice the furnace is not operating, I check the thermostat and it is on but no matter how high I raise the temperature nothing happens.

[howson]

Howard, I'm actually talking about the furnace fuse in the 12vdc panel. I haven't touched the thermostat at this point. If I remove that 15a fuse and put it back in the furnace restarts. Interestingly though, when I notice the furnace is not operating, I check the thermostat and it is on but no matter how high I raise the temperature nothing happens.

OK. When you pull that fuse the thermostat loses power, right?

What thermostat is installed in your Imagine? (I'd still start by attempting to isolate the problem to the thermostat or the furnace.)

[familytruckster4]

I cant help but ask if there is an adequate supply of propane ? It almost sounds like the furnace isnt lighting and then times out.

[howson]

I cant help but ask if there is an adequate supply of propane ? It almost sounds like the furnace isnt lighting and then times out.

If that was the case the DSI light should be lit on the Control Panel indicating the furnace tried three tries to start but did not sense an ignition. However, pulling the fuse would have the same effect (cycling the furnace) as resetting the thermostat, so...

Edit: The above is incorrect as the DSI light is associated with the water heater, not the furnace. The furnace goes into lockout without any visual indication. See post 13 for a full correction.

Paul & Deb -- did you try cycling the furnace off and then back on (using the thermostat) instead of pulling the fuse?

[Paul & Deb]

If that was the case the DSI light should be lit on the Control Panel indicating the furnace tried three tries to start but did not sense an ignition. However, pulling the fuse would have the same effect (cycling the furnace) as resetting the thermostat, so...

Paul & Deb -- did you try cycling the furnace off and then back on (using the thermostat) instead of pulling the fuse?

No, I didn't but it has now worked for 36 hours without reoccurrence so I may watch it for a while. I did swap the propane bottles but that doesn't make sense to be the problem to me. In previous trailers I could hear the furnace attempt to light at least 3 times before it would time out if the propane was depleted. I know this furnace is 10 times quieter than the crappy Atwood in our Reflection but man oh man! I never heard this try once until I reseated the fuse.

Mystery to me but I'll stay in watch mode for now and assume it was the propane.

Thanks all!

Camp on.

[howson]

Mystery to me but I'll stay in watch mode for now and assume it was the propane.

I confused the water heater with the furnace -- the DSI light is associated with the water heater, not the furnace. (Oops) The furnace does goes into a "lockout" if it tries three times without lighting, so it could very well have been associated with the propane container. Cycling the thermostat off and on should have had the same effect as pulling the fuse.

[Scott'n'Wendy]

Mark the LP bottle you removed that was installed when you had issues. Refill and put it back in service. See if your furnace problems return. It's possible the safety valve of the LP bottle restricted the flow enough to just be on the edge of enough flow for the furnace. Once the flow is a touch too low, the furnace flames out and locks out.

[howson]

Mark the LP bottle you removed that was installed when you had issues. Refill and put it back in service. See if your furnace problems return. It's possible the safety valve of the LP bottle restricted the flow enough to just be on the edge of enough flow for the furnace. Once the flow is a touch too low, the furnace flames out and locks out.

In an ASME tank...that could be true. (ASME tanks are typically in motorhomes.) For DOT cylinders (what we use in our trailers) the safety valve (the valve I *think* you're referencing) is in the pigtail not the cylinder itself. For those that don't know that term, the "pigtail" is the large knob and hose connection between the cylinder and two-stage regulator.

Arrow below points to the valve I'm referencing that's in the pigtail. (Before I went to the school I had no idea it was in the pigtail!)