Things to double-check if you have a gas-furnace issue.

System not running:

  • Check to make sure that your control or thermostat is set in the HEAT position. (You’d be surprised; often that’s the problem.) Make sure that the temperature is set warmer than the current indoor temperature. If it isn’t, your system won’t know to provide heating.

  • Ensure that your furnace’s power is on. Try turning the fan to ON using the fan switch on the control or thermostat to test for power to the furnace.

  • Check the circuit breakers in your home’s circuit breaker box (electrical panel) to make sure they’re in the ON position.

  • Check the furnace power switch to be sure it’s in the ON position (it looks like a light switch on a gray box located at the furnace).


System not heating enough:

  • Check the filter for buildup. If you have one-inch thick furnace filters, a once-a-month change is recommended. Two-inch-thick filters—and other high-capacity pleated filters—usually only need to be changed every other month or less, depending on the type. If you don’t change it, the filter will eventually become so full, it will block the proper airflow and strain your furnace.

  • Check all return air grilles to make sure they are not blocked. Return air grilles are larger and are located on a wall or the ceiling in newer homes. Older homes frequently have return air grilles on the floor.

  • Check all supply registers to make sure they are open and blowing air.


Other signs that may indicate a service call may be in order:

  • You hear your indoor-unit fan coming on but the air from the registers isn’t warm or the fan is turning on and off more frequently than usual. NOTE: If your system control has a “Constant ON” feature, you will not always feel warmth, even though air may be blowing.