Furnace Blowing Cold Air

Cold air at the vents means the fan side still works and the heat side quit, so call before the house drops much further.

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When this becomes an emergency

Registers are pushing air that feels cooler than the room it's blowing into.
The fan keeps running long after the burner should have brought it up to temperature.
Ignition attempts repeat in a pattern and then everything goes quiet.
There's a whiff of unburned fuel each time the blower starts.

What a pro does

Cool air at the registers is a burner story, not a blower story. A technician watches a full call for heat to see whether ignition actually happens, checks the ignitor and the flame sensor for the film of oxidation that makes a control board believe no flame exists, and pulls the fault history to find out how many failed tries came before the lockout. Oil equipment throws the same symptom from a worn nozzle or a pump that's lost pressure. Repeatedly resetting a locked-out unit stacks unburned fuel in the chamber. That's the part worth not doing.

Frequently asked questions

Why does the fan keep running if the burner isn't lit?

Many controls run the blower through a lockout so the house keeps circulating air and any residual heat gets used, which makes a dead burner feel like a fan stuck on.

Could a filter that hasn't been changed all season do this?

Indirectly. Choked return air makes the heat exchanger run hot, a limit switch cuts the burner, and what's left is a fan pushing cool air around.

Does this happen more on some kinds of equipment?

Older oil furnaces show it often, usually intermittently, because nozzle wear and fuel pump pressure both drift rather than fail all at once.

Is there harm in letting it keep trying?

Leaving a call for heat active while ignition fails cycle after cycle isn't good for the ignitor or the gas valve, and it won't solve anything on its own.

Furnace Blowing Cold Air?

Get connected with a local pro now.

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