How to Quiet a Furnace That Runs Constantly

A furnace’s fan draws air into the heat exchanger to be heated, which is then sent to the ducts for distribution throughout the house. The fan should turn off at the end of the heating cycle, so something is wrong if it runs non-stop whether your furnace is heating or not.

Fortunately this problem isn’t too complicated, and the average homeowner can usually solve it without professional assistance. Most heating and cooling experts attest that the likely suspects behind this problem are those listed below:

When Your Furnace Runs Constantly and Is Producing Heat


  • The Thermostat Fan Setting Is Incorrect


Check if your thermostat fan is set to AUTO. If it’s set to ON, the blower fan won’t quit even after a heating cycle ends.


  • The Fan Limit Switch Is Set to Manual Override


If the thermostat fan setting is correct, check the fan limit switch (a white button) under the hood of your heating unit. It controls how the blower fan behaves based on the temperature of the burners, but it only works when pressed in. If the switch is pressed in, it’s been set to manual override, which is forcing the fan to run endlessly.

Pull the fan limit switch out, and the furnace should quiet down unless the thermostat demands more heat.

When Your Furnace Runs Continuously But Still Isn’t Heating Your Space Adequately


  • The Thermostat Temperature Setting Is Too High


If you set your device to a temperature lower than the current temperature of the room, your furnace should stop running. If it does, it means your thermostat is set too high, and your heating unit is struggling to meet the temperature level that is asked of it. Make sure that your thermostat setting is  somewhere between 68°F and 72°F to prevent this from happening again.


  • The Air Filter Is Clogged


A continuously running furnace can also be caused by an airflow problem. If you haven’t washed or replaced your furnace’s filter lately, clean it or install a fresh one and see if that takes care of the issue.


  • The Ducts Are Leaky


If you also hear a hissing sound as your furnace is running, you probably have leaky ductwork. These breaks in your ducts need to be located and sealed, so the heated air will not escape through the gaps before it can reach the rooms it’s meant to warm up.

Contact a Heating and Cooling Technician to Solve Your Furnace Problem

If you can’t fix the issue yourself, leave it in the hands of a qualified heating and cooling technician from Reliable AC & Heat. Call us at (818) 423-4285 now to request service.

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