Furnace - Works Sometimes

JerJ-KEY

New Member
Joined
Jan 14, 2025
Messages
1
Location
Guelph
Good morning,

I have a 2007 Sprinter 311BHS. It’s been great for our family however it recently has been having issues with the furnace only working for periods of time (a couple days). We are in a permanent location and fully off grid and currently power with a solar / generator combination. So service is very difficult. The furnace has been fully taken apart, sail switch is free and clean. Igniter is clean and audibly working. This weekend we went in on Friday. It started right up and worked as it should. For the next day it switched itself on and off based on the thermostat and worked as it should. Then sat night I awoke to hear the clicking of the igniter but the furnace didn’t light. House batteries were at 13.1 V at this time. I took the exterior cover off to have a look and everything appears connected and when trying to restart a faint scent of propane was present to I would assume that means the solenoid is working? So if you have any thoughts I’d greatly appreciate it! Short of removing it fully and taking it in for service inspection. Thanks!!
 
Welcome to the forum :wlcm:

Make and model of furnace?

It could be the control board, it could be a sticky gas valve, it could be a bad gap on the igniter.
 
Welcome aboard! Furnaces are a bugger this time of year...lots of failures. Sadly, there are a few different thing that can cause the failures you've mentioned. The fact that you're smelling propane tells me that the Limit Switch and Sail Switch are both working OK.

In no particular order:
  • Fuse - with the age of your trailer I doubt you have a resettable fuse but it's easy to make sure you don't. If your fuse is black then replace it with a standard blue 15a fuse.
  • Connections - give all of the various connections a wiggle to make sure they are all making good contact.
  • Thermostat - can be faulty. I would bypass the thermostat feeds to the furnace to see if it runs until I disconnect it. Bypassing the Tstat should cause the furnace to run non-stop since it's now directly connected to power with no switch. Fairly easy to test.
  • Main Board - can also be faulty. This one might cost money to find out, though. Without the proper equipment to test it you typically just have to buy a replacement one and try it. This a likely culprit since the Main Board also contains the igniter. If you're getting propane and no ignition this is where I'd focus.
  • Propane Regulator - can also be faulty. It can work normally for other propane appliances but fail to consistently provide the volume of propane required by the furnace. I've had to replace this 3 times on 2 trailers.

These furnaces are fairly simple creatures but can sometimes be a pain to properly diagnose. This is a low-hanging-fruit list. Look at these and let us know how it's going. Reporting exactly what it does, and in what order, will be helpful in more diagnosis.

In my mind buying parts as a troubleshooting method is a good way to collect a backup supply for future failures. Our furnace has failed 3 times since new. I now have every replaceable part so I don't get stuck without a furnace in cold weather. YMMV
 
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Another possible contributing factor could be the temperature of your propane tanks. I don't know where your trailer is located or the temperature there, but on most travel trailers, the propane tanks are on the trailer tongue, exposed to the outside temperature. If you're in Guelph, Ontario and your furnace worked in the early afternoon/evening, but you woke up in the "wee hours of the morning" (when the temperature is at its lowest point) then you might be experiencing a limited "propane evaporation" due to cold temperatures...

Obviously, if you're wintering in Florida or in New Mexico, this wouldn't be as high on the list of possibilities, but if you're in Guelph and it's -5F, your propane tanks may be evaporating enough gas to support a couple of stovetop burners or even 18K BTU for the water heater but not enough evaporation to support 35K BTU for the furnace when the outside temperature is at its lowest....

While this might not be your problem, being in northern Michigan, I've seen several trailers with 20 pound and 30 pound vertical propane tanks that "fizzled out on the coldest nights".... One solution is a heat tape on the tank, another is an insulation blanket to help protect the tank from the extreme temperatures.

Additionally, on an "older trailer with OEM equipment" condensation and water contamination in the low pressure propane plumbing/regulator chambers might be freezing and blocking full low pressure propane flow to the furnace.

This might not be your issue, but certainly worth considering if you're in extremely cold weather.
 
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Here's my "take" on your problem. You say you are "off grid". You mentioned solar and generator. And, you say sometimes the furnace works and sometimes it does not. So, I'm assuming you are charging your batteries with solar and a generator (or is your generator a solar generator ... a glorified battery?)

Here's the problem. If the battery (12 volt DC) is low, the fan on the furnace will not run at full speed. If the fan is not running at full speed, there is not enough air flow blowing over your sail switch to activate it.

Sometimes, you battery has had enough time to charge to the capacity required for the furnace fan to start blowing with enough "umph" to activate the sale switch, and sometimes its not charged enough causing the fan to run slower and therefore the switch is not activated.

If you were plugged into shore power you would not have this problem as the flow of electricity is always steady and consistent, keeping keeping a steady flow from your converter and battery combination. When you are not plugged into shore power, the battery will deplete. When it reaches a certain point, it's not got enough charge to run the furnace properly.

That is the reason sometimes the furnace works and sometimes it does not, or it may run for a while and then stop working. The battery is discharging.

It's just that simple. You do not have any problems or issues. It's just a depleting battery thats not charged enough after a certain point to keep the furnace running.
 
Here's my "take" on your problem. You say you are "off grid". You mentioned solar and generator. And, you say sometimes the furnace works and sometimes it does not. So, I'm assuming you are charging your batteries with solar and a generator (or is your generator a solar generator ... a glorified battery?)

Here's the problem. If the battery (12 volt DC) is low, the fan on the furnace will not run at full speed. If the fan is not running at full speed, there is not enough air flow blowing over your sail switch to activate it.

Sometimes, you battery has had enough time to charge to the capacity required for the furnace fan to start blowing with enough "umph" to activate the sale switch, and sometimes its not charged enough causing the fan to run slower and therefore the switch is not activated.

If you were plugged into shore power you would not have this problem as the flow of electricity is always steady and consistent, keeping keeping a steady flow from your converter and battery combination. When you are not plugged into shore power, the battery will deplete. When it reaches a certain point, it's not got enough charge to run the furnace properly.

That is the reason sometimes the furnace works and sometimes it does not, or it may run for a while and then stop working. The battery is discharging.

It's just that simple. You do not have any problems or issues. It's just a depleting battery thats not charged enough after a certain point to keep the furnace running.

OP is getting ignition as he stated he can hear the clicking, that would rule out low batteries and not enough air flow on the sail switch.
 
Have you check the LP supply? As was discussed earlier, if it's very cold then the propane will not boil off into a gas. If the tank is level is very low then the issue is exasperated. Does the water heater work on lP ok? Light all stove top burners and check for a strong, sturdy blue flame.
 
Furnace

2014 cougar 333MKS. Not sure what model the furnace is but the thermostat on the wall is Dometic.
We recently started having issues with the furnace. It will run in the morning for a short period but than shut off and won't turn back on. It has been in the mid to high 20's where we live. The stove and water heater are still working. We had put a 5 lb tank on it and after that it has been having issues even though we now have 8 lb tanks on it.
 

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