Most heating system failures are caused by thermostat malfunctions, a tripped circuit breaker or blown fuse, or—in the case of combustion furnaces—a pilot light that has gone out. If the heat doesn't come on even when you adjust the thermostat to a setting above room temperature:

1) Be sure the thermostat is set to "Heat" (if yours is a heating and cooling system).

2) Be sure the furnace's circuit breaker is on or that its fuse has not blown. Check both the main electrical panel and any secondary sub-panels that supply power to the unit. If the circuit has blown or tripped, reset the circuit breaker or replace the fuse. If the circuit blows again, there is a probably a short in the electrical system providing power to the furnace. Either call an electrical contractor or see here for electrical repairs.

3) Be sure the furnace's power switch is turned on; it is usually located next to or inside the furnace cabinet. If it isn't on, turn it on, and wait for the furnace to engage.

4) The motor may need to be reset because of an overload. Look for a "Reset" button near the blower motor's housing and, if you find one, press it. If nothing happens, wait about 30 minutes for the motor to cool, and then try the "Reset" button again.

5) Turn off the power to the furnace at the main electrical panel or sub-panel. Look for a fuse in the power switch. If there is one there, it may have blown. Replace the fuse (be sure to follow the instructions in your owner's manual). If you don't have an owners's manual or are unclear about what it will take to do this, call a furnace repair technician.

6) With a gas furnace, the pilot light may have gone out or the gas valve may be shut off. Check the furnace's ignition.

7) If it still doesn't work, be sure the thermostat isn't faulty.

8) If none of this works, call a heating contractor or furnace repair technician.

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