Furnace not working or no heat? Check the thermostat, breaker, filter, gas valve and flame sensor - plus when to stop resetting and call for furnace repair.
Thermostat on Heat with fresh batteries; furnace power switch on; breaker not tripped; filter not clogged. These four account for a large share of no-heat calls.
Make sure the gas valve at the furnace is open and other gas appliances still work. If nothing gas-fired works, call your utility.
A healthy furnace draws (inducer), proves pressure, glows the igniter, opens the gas valve, lights, then starts the blower. Whichever step it stalls on tells the technician exactly which component failed.
Almost always a dirty flame sensor, a blocked flue, or an overheating limit switch caused by restricted airflow.
The burners are not firing or the furnace has locked out. Do not keep resetting it — repeated lockouts on a failing furnace are a carbon monoxide risk.
Do not bypass a safety switch, do not tape over a limit, and never heat a home with a gas range, grill, or generator indoors. If you smell gas or exhaust, leave and call 911 and your gas utility from outside.
Guesswork costs more than a service call. Talk to a licensed technician now.
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