“My RV furnace isn’t working!” is a common distress signal across many RV forums and Facebook groups. I’ll bet $100 that the first (and second) response to this SOS will be, “Check your sail switch. Probably needs replaced.”

Is this advice accurate? Is the furnace sail switch the suicidal culprit it’s so often made out to be? Or has this stereotyped, unloved part just been misunderstood?

What Is a Furnace Sail Switch?

A sail switch, also known as an air prover switch, is a normally open switch that closes in the presence of sufficient airflow. It looks like this (or quite similar):