My furnace is not working properly. When I turn up the thermostat, it will kick on but then turns off before reaching the desired temperature. I’m thinking that the issue is with the thermostat. Is there anything I can do to fix it? Thank you. —Chiara, 2020 Forest River Wildwood 40FDEN
First a question or, rather, clarification. You state “When I turn up the thermostat….” So, does the furnace work as designed when you leave the thermostat at a set temperature? For example, if you have it set for 68 degrees and it works fine, but you turn it up to 74 because it’s a little cold and then it starts and stops?
The reason for this question is, if the furnace works at the set temperature consistently and shuts off when set to a higher temperature, it would probably be the temperature sensor at the back end of the furnace.
How a thermostat and furnace work
I know we have covered this before, so bear with me, my readers! The thermostat is only an open and closed circuit provider. When you select a temperature and the ambient temperature drops below that setting at +/- 2 degrees, the thermostat closes. That sends the 12-volt power to the module board similar to touching two wires together.
The module board starts the blower fan to exhaust any fumes in the chamber outside and also pulls interior air from the coach through the air returns. The air flow going out the interior air chamber to the vents passes over a sail switch that must be lifted to verify there is enough power and airflow to open the gas valve and light.
The module then opens the gas valve, creates a spark, and starts a flame in the burner assembly. The air passes over it and flows to the vents inside the rig. At the end of the burner assembly is a high limit switch. That is a temperature sensor that regulates the temperature. If it gets too high, it will shut off.
If the thermostat is bad, you can verify by pulling off and connecting the wires directly. I’m not sure which model you have in your rig. However, you should have an owner’s manual with a basic wiring diagram. If you connect the wires and it runs, it is the thermostat. If it continues to shut off, it’s most likely the high limit switch.
One more thing to check. Make sure all your vents are open and not covered. Also, if you have the “elephant trunk” hoses, make sure they are not pinched or kinked. If you have a few vents closed, covered, or obstructed, the airflow will be restricted and might create a high temperature back at the high limit switch.
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.
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