A furnace not working on a cold morning often has a simple cause. This furnace troubleshooting guide covers safe checks homeowners and business owners can do and when it's time to call a technician.
Why Is My Furnace Not Working With the Heat On?
Start at the thermostat, since a wrong setting can make a healthy furnace look broken. A furnace blowing cold air may have its fan set to “On,” which runs even while the burners are off. Confirm these five settings:
- The mode is set to “Heat.”
- The set temperature is higher than the room temperature.
- The fan is set to “Auto.”
- The display is lit, and the batteries are fresh.
- No programmed schedule or after-hours setback is lowering the temperature.
If the thermostat calls for heat and nothing happens, the furnace isn't working.
Can a Dirty Filter Shut Down a Furnace?
Yes. A clogged filter restricts airflow until the furnace overheats and a safety switch shuts off the burners, which is one reason a furnace keeps shutting off. The U.S. Department of Energy recommends cleaning or replacing filters monthly during peak heating season and notes that regular maintenance can cut heating and cooling costs by 10% or more. If a new filter doesn’t help, call a technician.
Did a Breaker or Power Switch Shut It Off?
Before assuming the worst about a furnace not working, check the power, since even gas furnaces need electricity. A furnace that won't turn on at all may have a tripped breaker or a service switch near the unit that was accidentally flipped off. Reset the breaker once. If it trips again, call a professional, because a repeat trip points to an electrical fault.
Is It Safe to Check the Pilot Light or Igniter?
Looking is safe, but adjusting gas parts is not. Older furnaces show a steady blue pilot flame, while many newer models use an electronic igniter that glows or clicks at startup. If a furnace igniter isn't working or a pilot won’t stay lit, call a technician instead of restarting it repeatedly. If you smell gas, the U.S. Consumer Product Safety Commission (CPSC) advises you to leave immediately and call the gas company from outside your home, without using lights or phones.
Is a Clogged Vent or Condensate Line to Blame?
High-efficiency furnaces vent exhaust through plastic pipes and drain water through a condensate line. If snow or debris blocks the vent, or the drain backs up, a safety sensor shuts the furnace down. The CPSC recommends clearing snow from outside vents to keep carbon monoxide from building up indoors. According to the Centers for Disease Control and Prevention, more than 400 Americans die each year from unintentional, non-fire carbon monoxide poisoning. The CDC also recommends servicing gas-burning heating systems every year. If a carbon monoxide alarm sounds, get everyone outside and call 911.
If your furnace still isn't working after these checks, Harris Heating & Air is ready to help homeowners and businesses across Joplin and Webb City, Missouri. Our seasonal HVAC checks catch worn igniters and blocked vents before they leave you without heat, and our technicians repair what has already failed. Call Harris Heating & Air today to schedule your seasonal HVAC check or an HVAC repair before the next cold snap.
Pittsburg, Kansas: 620 235-9117
Webb City, Missouri: (417) 310-0132