If your RV furnace fan won’t turn off, there are some simple quick checks you do. The likely cause of your furnace fan always being on could be as simple as having your thermostat fan setting to “on” instead of “auto”. Other likely issues are a defective thermostat, a faulty wire connection, or a fan limit switch. In this post, we will review the most common causes, including:
- Thermostat Fan Setting
- Thermostat Temp Setting
- Defective Thermostat
- Wiring
- Fan Limit Switch
Let’s start with the most common reason why the RV furnace fan won’t turn off. I always like to start with the simplest and most obvious fix when troubleshooting a problem.
The good news is that your furnace is running, and this is likely a control issue that could be at the thermostat.
Table of Contents
- Thermostat Fan Setting
- Thermostat Temp Setting
- Defective Thermostat
- Wiring
- Fan Limit Switch
- Final Thoughts
Thermostat Fan Setting
Check your thermostat fan setting. You should have the option of a fan setting for “auto” or “on”. When the fan is set to “auto”, the blower fan will only run when there is a signal for heat. Once the thermostat reaches the specified temperature, the heat changer will shut off, and the fan motor will also turn off.
When the fan is set to “on”, the furnace blower will constantly run regardless of the thermostat heat setting or if the heat exchanger is producing heat. The fan never turns off in this setting and provides cold or warm air as needed.
Most people keep the fan on the “auto” setting, so the furnace blower motor only turns on with the heat exchanger to provide warm air.
Keeping the fan in the ‘On” position is a good option if you want to keep air circulating or at night to keep the noise down from the blower fan turning on and off throughout the night.
Thermostat Temp Setting
Another common issue is the temperature setting of the thermostat. If your desired temperature is set higher than the RV space temperature, the furnace and the furnace fan will continue to run until the set temperature is met.
The thing to remember is that an RV is not as thermally efficient as a home. A home will have walls with insulation at 3 ½” thick and insulated windows. The heat created in a home furnace can usually stick around a while before going out into the cold.
On the other hand, an RV is much less efficient. The walls are only 1 ½” thick, and the windows are not insulated. This means you will lose heat very quickly in an RV.
If your thermostat is set to a high temperature, the furnace may have difficulty keeping up with the heat being lost through the walls and windows. If this is the case, your furnace fan will continue to run with warm air to meet the set temperature.
Solution
Lower your temperature setting on the thermostat. Give it a minute and see if the furnace and fan turn off. If so, the temperature was set too high, and your furnace could not meet the demand. If this is the case, you may need supplemental heat, such as a space heater for added heat.
Defective Thermostat
The next potential issue on your RV furnace fan on all the time is a defective thermostat. If there is any issue with the thermostat itself, it could give false readings and cause the fan to always stay on.
A thermostat is a switch (like a light switch) that is automatically turned on and off by temperature. If there is any fault with the thermostat, the switch to turn on and off will not function properly, and you could have your fan stuck in the on position.
Wiring
Your RV furnace is controlled by low-voltage wires from the furnace to the thermostat. A couple of those wires will tell the furnace blower to turn on.
When your fan is set in the “auto” position, those wires going to the thermostat switch together, and the blower motor will turn on. Similar to the “on” position, the wire switch will always be set to run the blower.
If there is an issue with the wiring, like two wires touching, it could switch the blower motor to the “on” position even though the thermostat is set differently.
Check Wires
To check the wires at the thermostat, see if any of the wires are touching any other wires or screws. No wire should touch another wire or other metal in the thermostat.
If you see a wire touching more than one metal contact, reconnect it so it is securely only on one connector.
Fan Limit Switch
Inside your furnace is a fan limit switch. This limit switch is a thermostat inside the furnace to regulate the hot air and when to turn on the fan.
When you turn on your RV furnace, the signal from your thermostat tells the heat exchanger to turn on and produce heat. Once the heat reaches a specific temperature, the fan limit switch will signal the blower motor to turn on.
Also, when you turn off your furnace, the heat exchanger will turn off, but the fan will continue to blow out that warm air since there is still some heat. Once the temperature drops and all that is left is cool air, the fan limit switch will turn off the blower motor,
If your fan limit switch is defective and not working correctly, it can cause issues, like your fan not turning off.
Final Thoughts
Is your RV furnace fan always on and blowing cold air? Your RV heating system is controlled by your thermostat and controls the fan. If your RV furnace fan won’t turn off, the most common issue is the fan set to “on” instead of “auto”. Other things to check are your thermostat temperature setting and wiring. If everything looks good at the thermostat, the issue could be a faulty furnace fan limit switch.
Tony is an avid camper and RV traveler. He fell in love with camping on his first RV trip with his wife over 25 years ago. Tony loves sharing lessons learned and tips about RV maintenance and safe traveling.