5 Things To Check If Your Furnace Suddenly Blows Cold Air

It's not uncommon for a furnace to suddenly turn a cold shoulder when it comes to heating your home. Nevertheless, you'll want this problem diagnosed and repaired before it results in a cold, sleepless night for you and others in your home. Here are a few areas to check if and when your furnace suddenly develops cold feet over heating your home properly.

Circuit Breaker

A tripped circuit breaker is one common reason for a furnace to suddenly start putting out cold air. Locate the assigned circuit breaker for your HVAC system and see if one of the breaker switches has been tripped to the "OFF" position. If this has happened, reset it by turning it to the "ON" position and keep a close eye on the switch. If it trips again later on, have your HVAC technician inspect the furnace for electrical issues.

Pilot Light

If you're using an older furnace and the pilot light suddenly goes out, it could be due to a number of factors. Check the pilot light for signs of soot buildup and clean it, if necessary, with a stiff wire brush and compressed air. Also make sure there aren't any nearby drafts that are blowing your pilot light out.

Air Filter

Take a close look at the air filter and make sure it isn't clogged with debris. If so, replace the clogged filter with a fresh replacement as soon as possible. Clogged furnace filters can make the furnace overheat due to the lack of good airflow, eventually stopping the furnace from blowing warm air. All air filters should be replaced at least every 3 months.


Make sure your thermostat is using the correct settings ("heat" for the heating/cooling mode and "auto" for the fan speed) while the furnace is active. Also remember that the furnace will work only when room temperatures fall below the requested temperature set on the thermostat. Also make sure the thermostat has a fresh, working battery and that it's wired correctly to the furnace.

Flame Sensor

Check the flame sensor for any signs of carbon buildup. Your furnace won't operate correctly if the flame sensor can't detect the presence of a burner flame due to an excess coating of carbon. Use light-grit sandpaper to remove the carbon buildup from the sensor rod and then wipe it down with a clean paper towel. You may need to replace the sensor altogether if you're still experiencing problems afterwards. For more information, talk to a professional like Nebraska Heating & Air.