Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the RV Handbook and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses an RV furnace that won’t light.
Dear Dave,
We own a 2020 Minnie Winnie and pretty much love it. First couple of AZ winter uses the furnace worked perfectly. Now we are on an extended cross-country road trip and while in Colorado at high altitude we attempted to take the morning chill off with the furnace. The thermostat and blower fan seem fine but the burner does not fire up. Because of the young age of this unit I am wondering if it has a recall or bulletin on the furnace. TIA for any insight. —Don
Dear Don,
To help identify what might be causing your furnace to not light, it’s important to understand the operation.
Page Contents
How the furnace operates
When the thermostat is set and calls for heat, the fan motor starts and blows air to clean out or exhaust the burner assembly. The fan speed needs to be high enough to raise the sail switch inside the fan cage. That closes the circuit and tells the module board it is OK to open the gas valve and spark to light the burner.
If your battery is low, the fan will still turn but not with enough force to raise the switch, so it’s deceiving to owners. Even if you are plugged in to shoreline power, if your battery is sulfated, it will drop energy storage immediately and the converter may not kick in in a timely manner.
Another issue could be an obstruction in your vent lines or vents. If you have any vents closed or covered with rugs, this will restrict the air flow and cause a backup. That means the fan can’t lift the sail switch as well. Not sure if your Minnie has hoses like the photo or ducted vents under the floor with floor vents.
Recommendations
The first thing I would recommend is checking all the vents and lines inside the rig to make sure they are clear and allow air flow. Next listen for the click of the gas valve and a sparking attempt. If there is no spark attempt, then try boosting the battery with a portable battery charger/booster. If this does not help, the next step is to remove the fan cover and test the sail switch. This can be done with a multi-meter and push the sail switch up to check for a closed circuit.
Read more from Dave here.
Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.
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Down thru the years we have had to replace several circuit boards on our propane heaters. Best to have a tech check it out. Propane is dangerous…
This past winter while traveling in an unusually cold Texas, my furnace had a similar failure. Turned out to be a second switch in the furnace that senses that the ignition was successful. Replaced it, solved it. But that is just ONE of the possibilities among tbe others discussed here. I kinda like the high altitude as a prime suspect, but best of luck to you.
How about a spider web blocking the flame? Spiders seem attracted to smell of propane. We had that problem on our water heater.
Of course, if the furnace works at lower altitude, that would rule out an obstruction like a web.
Should ask if he has pets in the motorhome as hair and dust can clog the sail switch preventing it from moving to fire of the furnace.
At high elevation we had to take the outside cover off to get enough air for the furnace to kick on. I left the screws mostly undone so it was easier when we stayed in one spot, then tightened them down when we moved. Everything worked great once we got down into lower elevations.
Dave failed to mention the most obvious reason for a malfunction, since the Minnie Winnie is at high altitude in Colorado. At high altitude, propane appliances burn very poorly, because the orifice can’t feed enough propane to the burner. With low oxygen at high altitudes, the burner needs a larger orifice to get the proper propane/oxygen mix for efficient fuel burning. If you’re going to spend much time at high altitude, get a larger orifice to swap out while there. Changing it is easy. But then you’ll have to swap back to the original when returning to lower altitude.
My guess is throw rugs, women seem to think a floor isn’t complete with out rugs. Our previous motorhome had floor vents for the furnace, we had removed the carpet and installed vinyl flooring, then DW started putting down throw rugs. My recliner had a floor vent next to it and a rug was put by the chair covering the vent. I didn’t think much about it during the summer with a/c, but first chilly night the furnace wouldn’t work, finally it dawned on me check the rugs, sure enough uncovering two vents it started working. That’s why RV vents don’t have vent doors like homes do, in a home you can partially or completely close off a vent and the air just blows harder in the next one, not in an RV.
Fred, it needs more air not propane. I’ve had to adjust water heater and refer for more air flow at altitude.
My bad. I was trying to rush a comment before leaving the rv for the day & got my facts backwards.
I’m no expert, but seven years ago we went to Crater Lake NP, and our (then six year old) Georgetown Class A was sitting at Diamond Lake RV Resort (at about 5500ft altitude) and our Dometic Fridge, Suburban WH and Furnace operated fine. We did fill our propane tank before we left the Seattle area, and used the same tank all trip long, so I’d be curious if these folks issue is contaminated propane. The only issues I’ve ever had with any of my propane gear was when I tanked up at the local Co-op Supply instead of the actual propane distributor I normally go to (which is next to the storage yard where my RV is kept). The only other place I’ve needed propane was on a three week road trip, and we were able to fill up at a Costco in Mobile, AL, and that was due to us boondocking/Walmarting for the majority of the trip to Florida – and we never had any propane trouble on that trip.
In my rush to comment before leaving for the day, my brain reversed the process for adjusting heaters at high altitude. You need a smaller orifice to reduce the propane feed to get the proper fuel/air mixture at high altitudes. The air is thinner at high altitudes, thus requiring more air or less fuel to achieve the proper balance for an efficient burn.
Any problems with the other LP appliances? I’m wondering if it could be the butane-propane difference in LP dispensed in warm and cold climates. https://www.dependablelpgas.com/things-you-might-not-know-about-propane-gas/
Butane is not used in RVs primarily due to it being able to be frozen in sub freezing temperatures.
Sometimes in warm climates you may get a mix.