Heater blowing cold air in Herndon, VA

A heater blowing cold air in Herndon, VA is often a quick fix — but on gas furnaces it can also mean the burners genuinely aren't lighting, which is worth ruling out first.

Common causes

• Thermostat fan setting on "ON" instead of "AUTO" — the blower runs constantly, including whenever the system isn't actively heating (the most common cause, and the easiest to fix yourself)
• Pilot light out on an older gas furnace
• A dying flame sensor causing the burners to shut off seconds after lighting
• A clogged filter restricting airflow across the heat exchanger
• Heat pump in a normal defrost cycle — briefly blows cool air while defrosting the outdoor coil, then switches back

On a heat pump specifically, air that feels cool but isn't actually cold is often normal — heat pumps deliver air a bit below body temperature even when working correctly, which surprises a lot of people used to gas-furnace heat. Truly cold air, or air that stays cold for more than a few minutes, is the real signal something's wrong.

Check this first

Look at the thermostat's fan setting before calling anyone — switching it from "ON" to "AUTO" solves this more often than any other single fix.

Herndon HVAC contractors who handle heating diagnosis

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