You’ve got a nice, warm RV on a cold day, but you still hear something humming in the background. It’s not the fridge or another appliance because it’s a constant low hum that hasn’t turned off in some time.

Your RV furnace blower is still running, even after the furnace itself has stopped heating. Now it’s just pushing air around – which isn’t really a bad thing.

An RV furnace blows that runs continuously is a sign that either there is a hardware problem with your furnace, or that the system isn’t quite setup right.

The simple problem: your RV furnace settings

It’s possible that your RV furnace blower is still running because you are unknowingly telling it to. Thermostats both on and off furnaces tend to have just a couple of settings, but these are important in how your blower functions.

Most thermostats have a FAN switch that lets you choose between:

• Auto: Only runs your fan when the furnace is heating. If you have a heat pump, this setting might also work for cooling. This is generally the preferred choice for people with RV furnaces.
• On: The fan runs continuously, regardless of whether or not heating or cooling is running.

There are upsides and downsides to keeping your furnace on “On.” The upside is that you get continuously circulating air, which can be nice when it is especially warm or cold, or if your RV has circulation issues. Air won’t just hang around, it’ll get pushed. The downside is that a large fan running also will use more electricity – and hence more battery, gas, or shore power.

The issue you might be experiencing involves setting your fan to “On” by accident. Perhaps you were trying to refresh the air in your RV, or maybe you are in a thermostat fight with a family member or friend and don’t know it. We bring the wrong setting on a switch up first because it’s by far the easiest problem to fix. All you need to do is switch the RV fan setting to auto.

Bigger problems: Furnace fan limit switch

Your furnace likely has what’s called a Fan Limit Switch. This switch tells your fan to turn off when the furnace stops running, when the furnace has reached the temperature as requested by your thermostat.

The switch can go bad, like anything electronic. The solution here is to either find and clean the fan limit switch, or to just replace it. In some cases, a good do it yourselfer can replace the fan limit switch themselves after ordering the part. 

Another potential reason: thermostat wiring

The problem of poor thermostat wiring is more likely to come up right after you install a thermostat, but wires can come loose and problems pop up later.

The wiring from your thermostat to your furnace can be a bit complex, especially to people trying it for the first time. It’s entirely possible for a do it yourselfer to mix it up and not test everything – or for wires to gradually fade and just stop working.

While we can’t exactly provide a specific guide to checking all your wires because they do differ based on the thermostat and furnace, we suggest removing the thermostat from the wall and checking for obvious loose wires.

This is something you might want to consult with a service technician. It’s not dangerous to work on your thermostat, it just has a few things that could go wrong that make a solution less than obvious.

Your furnace is actually overheating

Sometimes problems are not quite what they seem. It’s possible for your blower to seem like it’s continuously running when the reality is that your furnace should be running too.

This is more common when something in your furnace is clogged, and causes the furnace to be unable to “breath.” A furnace obviously gets hot, but it actually can get too hot and shut down without turning off the fan immediately too.

Inspect your furnace exterior for excessive dust or debris. You should also check outside for your furnace vent to make sure it’s not clogged by debris, dust, or even animal nests.

Another symptom can be “short cycling” when your furnace turns on for a few minutes, then struggles to restart and turns on again after a while. This isn’t an issue with the fan, it’s the furnace!

Conclusion

Those are the primary reasons why your fan would continuously run. Some problems like this are simple and come from choosing (intentionally or unintentionally!) incorrect settings that create little problems and annoyances. Others are issues that come from wear and tear or incorrect setup.

If you can’t figure it out, consult a technician before tearing your furnace and thermostat apart. They are trained for these problems and have encountered problems hundreds of times – it might be worth it to get your fan to turn off sooner than later.

Finding one issue with your furnace also gives you a good reason to do some routine maintenance and give the vents a good cleaning to make sure you avoid future problems, too.