Furnace Doesn’t Work

Problem: Furnace is dead, or doesn’t turn on when the thermostat is raised.

Background: What are often thought to be furnace emergencies are caused by the thermostat being set or operated wrong, by having the power to the furnace cut off, or by not having fuel or a working pilot light. (Important: If you detect gas odor in your home or in the furnace area, take immediate precautions.

What to do: First double-check to be sure that power is reaching the furnace. Check the circuit breakers or fuses at the main service box. If reset breakers or replaced fuses blow again, call a service technician. Also check to see that any switches on or near the furnace are turned on. Be sure that the thermostat is set in the “heat” position, and that it is set above room temperature. If the furnace doesn’t come on after an interval, check the furnace itself. If you have a gas furnace, the gas valve should be turned to “on.” If you have an oil furnace, check the fuel level in the tank. If the furnace has a pilot light, check to make sure that it is lit. If not, relight it carefully, following the instructions in the owner’s manual or on the unit.

(Warning: If you smell gas, leave the area immediately and call a technician. The lighting instructions for a gas furnace should explain the procedure to use to determine whether the gas valve is good. If the test procedure indicates the gas valve is bad, turn off furnace gas valve and main gas valve and call a technician. Also call for help if the pilot light does not stay lit after several tries.)

Special advice: Most furnace controls will have a reset switch. If the furnace starts after the reset switch is pushed, but shuts off again, call a technician. Gas furnaces equipped with an electronic ignition device, instead of a pilot light, have a gas valve designed for slow opening. It first opens part way to let just enough gas through for safe ignition of the burners. After a few seconds it opens fully to allow proper flame height. The burners should light within 2 seconds after the gas valve opens. If air in the valve and lines prevents the flame from being established within 6 seconds or so, the system will go into “lock-out.” To reset, wait 1 minute and turn the thermostat to a setting below room temperature. Then turn back up to a setting above room temperature; this should re-start the ignition cycle.

Helpful hint: If the furnace works, but heat is not circulating, the problem may be with the blower or the blower belt. If the flame on burner is yellow or blue, or lifts off of the burner, call for a technician to adjust. Check your owner’s manual for annual maintenance suggestions and keep the furnace and its components free of lint or dirt accumulation.