FURNACE PROBLEM · DIAGNOSIS GUIDE
Your furnace is running but pushing cool air through the vents. Here are the most common causes and what to do about each one.
The most common 'cold air' call we get isn't a furnace problem — it's a thermostat setting. FAN runs the blower continuously, including when the burner isn't on. Switch it to AUTO and the cold air stops.
Modern furnaces have a pre-purge cycle that runs the blower for 30-60 seconds before the burner ignites. If you're catching it during this window, it's normal.
The blower runs but the burner won't light, so you get cold air. Igniter replacement: $150-$425.
Sounds obvious but worth checking — especially in extended cold snaps when propane gets used faster than expected.
If the furnace overheats (often due to a dirty filter or blocked airflow), the gas shuts off but the blower keeps running to cool the system. Replace the filter, let it reset, and see if it lights properly.
If basic checks (thermostat setting, filter, breaker, gas valve) don't fix the cold air, call us. A non-igniting furnace is usually a quick repair — igniter, flame sensor, or gas valve issue.
Call (973) 948-0680. Same-day appointments available, 24/7 emergency dispatch.
“Furnace running but blowing cold. Igniter was bad. $250 repair done same day. They explained everything and didn't try to push a new system.”
Erin D. · Denville, NJ
Same-day appointments in Sussex and Morris counties. 24/7 emergency dispatch — answered around the clock by a real on-call technician.
98 Morris Turnpike, Newton NJ · NJ HVACR Lic #19HC00108700 · Since 1999
At Constant Air, we specialize in delivering high-quality heating, ventilation, and air conditioning services that keep your home and business comfortable all year round.
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