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Green Bay Heating
Green Bay Heating
Heating · Wisconsin

Furnace Blowing Cold Air

Air moving without heat behind it means the burner side has stopped while the fan carries on, and that is worth a call today.

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When this becomes an emergency

What a pro does

Cool air at the registers is good news of a sort, because it proves the blower and the ducts are doing their part. A tech doesn't guess; he watches a full call for heat from the equipment side: inducer spins up, pressure switch proves, ignitor glows, gas valve opens, flame lights, sensor confirms. Whichever step stalls tells the story. A flame sensor coated in a film of oxide reads no flame within a couple of seconds and the board shuts the gas back down, which is easily the most common version of this. Lockouts follow, and the fan often keeps running through them. Sidewall vents packed with drifted snow will stall the sequence at the pressure switch instead, and that's a seasonal favorite here. Retrofitted duct runs in older two-story homes can also make weak, tempered air feel colder than it really is by the time it reaches an upstairs bedroom.

Frequently asked questions

That short burn followed by a shutdown is the signature of a flame-proving failure. The burner does light, but the control never gets confirmation it can trust, so it closes the valve.
The control runs the blower to pull the last usable heat out of the exchanger and to protect it from overheating. On a locked-out unit that same fan keeps circulating air with nothing warming it.
On a heat pump, yes, since output falls as it gets colder outside. On a gas furnace the supply air should be well above room temperature regardless of what the wind is doing.
Very. That flash pattern is a fault code, and reading it off before the call saves diagnostic time because it points straight at the step in the sequence that failed.

Furnace Blowing Cold Air?

Get connected with a local pro now.

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Keep going

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