Thermostat is calling for heat. The blower might run, but there's no flame and no warm air. Cold house.
You probably came here because…
- Thermostat set to Heat but you hear clicking and no flame
- Blower turns on but only cold air blows
- The furnace tries to start, stops, tries again, then locks out
- You may hear a clicking sound near the furnace
What’s actually happening
Modern furnaces have a startup sequence: draft inducer spins up, pressure switch closes, ignitor glows, gas valve opens, flame sensor confirms flame, main burner stays lit. Any one of those failing and no heat.
The four most common failures are: dead ignitor (hot surface ignitor cracked or worn out), dirty flame sensor (rod is coated and can't sense flame), stuck pressure switch (blocked flue or bad switch), or no gas (valve off, or empty propane tank).
If you have a heat pump instead of a gas furnace, the same 'no heat' symptom is a totally different diagnosis. Heat pumps have their own list of failure modes.
What we do about it
Check the thermostat and gas
Confirm it's set to Heat, not Emergency Heat or off. If you have propane, check the tank gauge. If natural gas, confirm the shutoff valve at the furnace is open (parallel to the pipe = open).
Reset the furnace
Turn the power switch off at the furnace (looks like a light switch on the side or nearby wall), wait 60 seconds, turn back on. Then set the thermostat to Heat and 5 degrees above room temp. Watch for the startup sequence.
Listen and count
You should hear: a hum (draft inducer), then a click (gas valve), then a whoosh (ignition), then the main blower after 30-60 seconds. If it stops at click-click-click with no whoosh, it's ignitor or flame sensor. If it never gets past the hum, it's pressure switch or the flue is blocked.
When to just call
If you smell gas at any point, do not try to relight anything. Get out of the house, call 911 or the gas company, then call us at (423) 637-1846 once you're safe. Otherwise, if the furnace is locking out and you're cold, we'll come out same day.
Ready to fix it?
Call the family that’s been doing this in the Sequatchie Valley since 1996.