Furnace Blowing Cold Air
When your furnace runs but the air coming out is cold, it usually means the burners are not staying lit or a safety control has shut down the heat. Some causes are simple; others need a technician. Here is how to tell.
Common Causes
Thermostat Set to “On”
With the fan set to ON instead of AUTO, it blows even between heating cycles, pushing room-temperature air. A quick setting check rules this out.
Flame Sensor or Ignitor Failure
A dirty flame sensor or cracked ignitor causes the burners to light and then shut off, so the blower pushes cold air.
Overheating / Clogged Filter
A clogged filter or blocked airflow trips the high-limit switch, cutting the burners while the fan keeps running.
Warning Signs
- !Air from vents is cool or room-temperature
- !Burners light briefly then go out
- !Frequent short cycling
- !A clicking ignition that never catches
How We Fix It
- 1Confirm thermostat settings and replace a dirty filter.
- 2Clean the flame sensor, inspect the ignitor, and check the high-limit and gas supply.
- 3Test a full heating cycle to confirm steady, warm output.
What It Costs
Most cold-air furnace repairs (flame sensor, ignitor, filter, controls) run $120-$600. Heat exchanger or gas valve issues are quoted after diagnosis.
If You Ignore It
A furnace that short cycles wears components fast, and some causes (like a cracked heat exchanger) are safety risks. Get it diagnosed before the cold snap leaves you without heat.
Frequently Asked Questions
Is cold air from the furnace dangerous?+
Can I fix it myself?+
Do you offer same-day heat repair?+
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