Friday, June 2, 2023


Why does my RV’s furnace only ignite when I lift the sail switch?

Dear Dave,
I have determined that my RV’s furnace blower airflow is not sufficient to activate the sail switch. The batteries are new and charged, but it will only ignite when the sail switch is depressed manually. There appears to be sufficient air blowing out of vents. I can’t see any blockages in lines or hoses, and there does not appear to be much dust on impeller blades. I am stuck and would appreciate any guidance. Thanks in advance. —Anthony, 2016 Bigfoot 25FB

Dear Anthony,
Even though the batteries are “new and charged,” have you tried using the furnace plugged into shore power? When you are plugged into shore power, the converter or whatever type of charger you have should be providing 13.2 volts at least, which would be sufficient for powering the blower motor and raising the sail switch. Put a multi-meter on the battery/batteries when attempting to start the unit and see if it stays at least at 12.6 volts.

Check vents and filter

If yes, inspect all the vents inside the rig to make sure they are all open and not covered with a rug or something else. Also check the cold air return to make sure it is not obstructed. Most cold air returns do not have a filter. However, I’ve learned never to say never when it comes to RVs! If there is a filter, try running it without to see if it has better air return and work.

You state that it works if you manually depress the sail switch, which is pictured above and is typically hard to get at in most rigs. There is not much of a test for an RV’s furnace sail switch, other than open and closed. I have heard in some cases there is enough dust or grit on the switch that it makes it difficult to lift. Try spraying the tab and switch body with CRC electrical cleaner and see if that helps. One other test would be to get an airflow meter such as this one on Amazon.

With this, you can get the actual airflow and verify with the manufacturer what it should be. If the unit is plugged in and getting proper voltage and the fan is not providing sufficient airflow, I would assume the motor is getting weak and needs to be rebuilt or replaced.

 You might also enjoy this from Dave 

Furnace issues: I’ve replaced the sail switch but now it runs intermittently – Why?

Dear Dave,
I had a sail switch installed in my Atwood furnace. Sometimes it runs great for three or four days, other times it won’t ignite but for a couple of seconds. What’s happening? —Ty

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberg
Dave Solberg 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. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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David Solberg
22 days ago

Just got an update from Anthony.
“Hi Dave. I appreciate it. It turned out that the problem was not the motor but in fact the sail switch not having to “expect bend” required to catch the wind off of the squirrel cage. This was discovered only after a tech came out to confirm the motor was in good working order.”

22 days ago

Not knowing what a sail switch looks like but in your picture I do see a micro switch with long arm on it! Wondering if thats the sail switch. If so wondering what makes contact with it too get the heater working!

David Solberg
22 days ago
Reply to  Snoopy

Yes, the micro switch with the metal blade is the sail switch. Air from the fan “lifts” the bar until the switch clicks or closes sending 12-volt power to the module board telling it there is enough fan speed to open the gas valve and light. If the sail switch doesn’t go high enough the fan will run and blow cold air.

22 days ago
Reply to  David Solberg

Hi Dave
Thanks for taking time to give me a great answer. I took a close look & noticed the metal bar is a lot wider than I thought. My mind process went right to a micro switch that I have in my shop that the metal bar is a lot smaller.
Now I understand.
Thank you

Ed K
22 days ago

I had the same issue and found the fan motor bearings were dry, a little electric motor oil and I was back in business. Been working for over 10 years now with no further problems.

Allen Cartee
22 days ago

This is great information to know – I was unaware of a sail switch.

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