Don't get left in the cold by a faulty furnace this winter.

By Nancy Mattia
December 05, 2019

A furnace that heats your home may be considered an appliance but unlike an oven or refrigerator, it's more likely to break down from time to time—usually on the coldest days of the year! Some furnace problems are easy enough to fix yourself; others need to be handled by a licensed HVAC contractor. If you're attempting to fix the problem on your own, always turn the furnace off before you start. "The benefit to turning off the furnace before working on it is to kill all power to that system to avoid getting electrocuted or blowing a fuse," says Brian Ivester, service manager, Andersen Heating and Cooling in Charlotte, North Carolina. (The furnace's switch may be on either of its sides; also turn off the furnace's circuit breaker). Here are five common problems and how to fix them.

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Related: Tips to Trim Your Electric Bill

Your thermostat isn't showing a readout.

There may be no readout because the thermostat is turned off; simply turn it to "heat" and set it at least five degrees above room temperature. If the thermostat is on but still not showing a readout, it may be set incorrectly. Check that it's turned to "heat," rather than "off" or "air."

The furnace is on but isn't blowing much hot air.

Your furnace's air filter is where dust and dirt collect, and it's most likely clogged. "There's a switch in the furnace that, if the furnace can't get enough air flow through the filter, will cause the furnace to turn off so it doesn't overheat or run too hot," says Mike Geddings, president of Panther Heating and Cooling in Rock Hill, South Carolina. The simple solution is to change the filter. Turn the thermostat to "off," locate the filter (sometimes behind a door or near the cooling system), remove the old filter, and replace with a new one. Turn the thermostat back on.

The pilot light won't turn on.

The culprit may be dirt buildup around the pilot light or a strong draft near the furnace. Follow detailed instructions (usually taped to the side of the furnace) that explains how to relight your particular model. Be sure to turn the gas off before attempting to fix anything. Once it's relit, the flame should be bright blue; if it's another color, call an HVAC contractor.

The furnace isn't inspected every year.

Furnaces need some TLC to maintain their vim and vigor and prevent problems. The best way to ensure that is to have an annual checkup, which should include cleaning various parts of the furnace. Ask your HVAC expert about buying an annual service contract—it may be economical if it includes an inspection once a year. When problems are caught early, a furnace will run more efficiently and last longer.

The furnace's circuit breaker has tripped.

When this happens, the flow of electricity is cut off to keep the circuit from overheating. You can easily reset the furnace's breaker (it's the one in the opposite direction of the others) by switching it to the full "off" position then switching it to "on," but first you should figure out the reason the furnace tripped the breaker. Often it's due to a dirty air filter.

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