Stop and read this first
If you smell gas, leave the house and call your utility's emergency line. Do not flip switches. Do not start the furnace.
Five things to check, in order
- Thermostat — set to Heat, raise the setpoint 3°C above room temperature. Replace batteries if the display is dim.
- Furnace power switch — looks like a light switch on or near the furnace. Confirm it's on.
- Breaker — find the furnace breaker in the panel. Flip fully off, then back on.
- Filter — pull it out. If you can't see light through it, replace it. A clogged filter trips the high-limit switch and shuts the furnace down.
- Condensate drain — high-efficiency furnaces shut off if the drain is blocked. Look for a clear PVC line; clear standing water with a wet/dry vac.
Still nothing?
Look for a small LED inside the furnace door — the blink pattern is a fault code. Take a photo. Most Canadian furnace brands (Carrier, Lennox, Goodman, Trane) document the codes on a sticker inside the door.
When to call a pro
- Pilot light won't stay lit on an older furnace
- Burner cycles on and off rapidly (short-cycling)
- Smell of burning electrical, hot plastic, or sulfur
- Furnace older than 15 years and no heat in winter — don't gamble
A Canadian HVAC service call runs $120–$200 plus parts. A new ignitor is ~$80 installed; a control board is $400–$700.