Furnace Blowing Cold Air

Air that comes out cool while the fan runs means the burner side quit and the fan did not, and that is a call worth making before the house falls behind the wind.

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When this becomes an emergency

Vents are moving plenty of air and none of it is warm.
The blower runs on and on without the house gaining ground.
You hear the burner try to light and then go quiet again.
The system stops responding until the power is cycled at the switch.

What a pro does

Cold supply air points squarely at the heat source rather than the fan. The technician verifies whether ignition actually occurs, examines the flame sensor and ignitor, and looks for a safety lockout holding the burner off while the blower keeps circulating for comfort. Draft is the local wrinkle worth checking too, since a strong gust across a sidewall vent can disturb the pressure switch enough to abort a call for heat on a healthy furnace. A system that has locked itself out is saying something, and overriding it repeatedly isn't the fix.

Frequently asked questions

Why does a small sensor stop the whole furnace?

The flame sensor is what proves fire to the control board. Coat it in residue and the board concludes there is no flame, so it closes the gas valve within a couple of seconds.

Can wind actually interrupt a furnace?

It can on sidewall-vented equipment. A gust that pressurizes the vent termination shows up at the pressure switch, and the board treats that as an unsafe condition and stops.

Does a dirty filter cause cold air?

More often it causes weak airflow, but the overheating that follows can trip a limit and give you the same complaint by a different route.

Should the thermostat be turned off in the meantime?

Setting it to off or to fan only is reasonable, since dozens of failed ignition attempts overnight put wear on parts for no return.

Furnace Blowing Cold Air?

Get connected with a local pro now.

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