Furnace cycling off and on frequently

[Guy from Cowtown]

Hi everyone. We are a 2020 3120RL. Our furnace has started cycling on and off frequently, i.e. kicks in, runs 10 seconds then cuts off for 10 seconds, on 10-off-10, and just keeps repeating until it reaches the desired inside temperature (at least we're warm) but its annoying as heck at night. I think I might have replace some kind of heat/ temp sensor or board? Anyone else ever have the same problem? Thanks in advance!!

[Bourbon County]

Most of the furnaces have 2 different fans in them. One is a draft induction blower that supplies air for combustion, this is the first thing you hear when the furnace gets a heat call. There is an air flow sensor for this blower to prove you have combustion air; these are a pretty common failure point and fairly easy to replace. If the furnace is actually lighting the burner, this is not your problem; the burner won't attempt to light without proof of air flow. There is a timer that will time out if you don't get air flow confirmation.

If the burner is lighting and then cycling off pretty quickly, it could well be a flame sensor. The mother board is another possibility, but I wouldn't think likely if it starts the ignition cycle and the main blower comes on. The other fan is the blower that actually circulates the warm air.

[jsb5717]

Could be a few different things. Could be the air flow sensor as stated above. It could also be your propane regulator. Ours was acting similarly until I replaced our OEM Fairview regulator with a Marshal Excelsior regulator. Less likely, it could be your thermostat. If it's a Dometic they can be finicky.

The fact that it's actually completing all of it's pre-ignition functions and firing before shutting down would point me toward the regulator

[Carl n Susan]

Not having a newer furnace and not knowing exactly when this came about, but there have been numerous reports that the cheap, poorly made, inferior, 15 amp self-resetting fuse for the furnace may cause this problem. Change to a standard blade fuse and the problem goes away?

[Bourbon County]

A quick easy check you could do is remove the exterior access cover and check for obstructions in the supply and exhaust. These areas are subject to obstruction by insect nests, leaves, and even sometimes small birds. This is the air path for combustion air and if they are restricted, I doubt you would get the airflow switch to make and the burner would ever fire.

Have you actually measured the 10 second intervals you mentioned, or is that just a guess? When the circulation blower comes on do you hear any unusual noises like a squealing sound? They use sleeve bearings in those motors and they tend to get pretty loud when they fail. A blower motor bearing failing might be enough to overload and drop out.

[steiny93]

could be tripping from the 'high limit switch'

When it cycles, does the fan continue to run but the burner is cycling? Or are you saying that the fan in cycling (stopping and restarting)?

If the fan runs continuously but the burner is cycling it could be that the switch is bad or you have an obstruction in the air way.

I'd recommend starting by verifying that all the ducts are opened and not restricted, it's common to have an air restriction cause this type of behavior, very common with fish houses.

[Arkware]

I second Carl's suggestion. The 12 volt re-setable fuse.
Had trouble with mine and replaced the fuse with a 'standard' fuse.
no trouble since.

[Wisconsin Retiree]

Not to change the subject but out of curiosity how loud are your furnaces? Aside from very noisy inside the trailer when I am outside my furnace sounds extremely loud to me? The guy next site even commented how it sounds like an industrial size furnace??? Are others as loud?

[jsb5717]

Originally Posted by Wisconsin Retiree

Not to change the subject but out of curiosity how loud are your furnaces? Aside from very noisy inside the trailer when I am outside my furnace sounds extremely loud to me? The guy next site even commented how it sounds like an industrial size furnace??? Are others as loud?

They're all loud. Some have said that the Suburbans might be a little quieter than the Atwoods but they are still loud. There are also different BTU furnace sizes, which will likely have show variable in volume. Ours is surprisingly quiet indoors, but that's due to placement and insulation between the furnace and living space. Outdoors ours still sounds like a blast furnace.

[Denali]

Sometimes it’s because the furnace is not getting gas. Turn on your gas stove and your gas hot water heater. Let them run and then try out your furnace. Also check your battery as the furnace get 12 volt power to operate. I try little things first

[DaveK]

We had the re-setting fuse problem as well.

We also had the control board replaced under warranty.

[nellie1289]

This is a timely post for me as well. We are out in our 2021 this weekend and i seem to be having similar issues. We have never really used our furnace before as we only go out in summer but it has been chilly here in the northwest. i do check the furnace exahust for pets and run it once in a while to make sure there is no issues. I put the thermostat to "heat/Electric" and the gas furnace definitely fires. You hear a fan kick on, then the furnace fire, then it blows heat for about 1 minute. The heat pump seems to turn on too. Then about a minute later it turns both off, and then both come back on and the process continues as the temperature slowly comes up. I have no idea what is wrong.

Also how come my thermostat sometimes shows "heat-gas" "heat gas-electric" and some times "heat-Electric". What im saying is sometimes "heat-electric" is not one of the toggle options.

I have the coleman airxcel thermostat and heat/pump air conditioners

[MOODY]

2020 Montana - furnace would come on & after 5-10 seconds the furnace would go out. The fan would continuously run. After 5-10 seconds the furnace would relight and after 5-10 seconds the furnace would go out again. This process would continue for 10-15 minutes before it would time out. Replaced to many parts to describe.
Finally found a memo that stated at point of installion that the furnace was carried by the propane line as a handle and slightly bent the line. Advised to push the line back and to the right slightly- 1/4 - 1/2 inch. Also read about oil in the propane lines.
Repositioned the fuel line. Disconnected the propane line at the bottom of the trailer where the flex line from the regulator attaches to steel pipe and at the furnace inlet. Blew out the line with compressed air at 100 psi. Did not notice any oil or debris.
Furnace works fantastic now. I have been having this problem for over a year. It used to work only with temps above 35 degrees but in the past 6 months has not worked at all.
Installed a drip line at the regulator to take care of any future oil contamination. Search for rv propane line oil contamination and you might be surprised at your findings.
My furnace always acted as if it was starving for fuel. Any repair I would start with blowing out the lines & then progress from there.