Why Is My Furnace Not Working?
If your furnace stopped working, check these in order: thermostat is set to HEAT with the temperature above room temp, air filter is not severely clogged, circuit breaker is not tripped, gas supply is on (check if other gas appliances work), and the furnace power switch is in the ON position. For newer furnaces, check the error code on the control board — blinking lights indicate specific problems.
THE DETAILS
Thermostat first. Make sure it is set to HEAT, the temperature is above the current room temp, and the batteries are not dead.
A clogged filter can cause the furnace to overheat and shut down as a safety measure. Replace it if dirty.
Check the circuit breaker and the power switch on or near the furnace. The power switch looks like a light switch and sometimes gets bumped off accidentally.
Make sure gas is flowing. If your stove and water heater work, gas supply is fine. If nothing gas-powered is working, call the gas company.
Modern furnaces have diagnostic LED codes on the control board. Open the access panel and look for blinking lights — the pattern tells a tech exactly what failed.
🔧 WHEN TO CALL A PRO
If you smell gas, leave the house immediately and call 911 or your gas company. For non-emergency situations, call a tech if the basic checks above do not resolve the issue.