A furnace blowing cold air is usually not broken in the expensive sense. The most common causes are a thermostat set to ON instead of AUTO, a dirty flame sensor shutting the burner down seconds after ignition, a clogged filter tripping the high-limit switch, a pilot or ignition fault, or a condensate blockage on a high-efficiency unit. Four of those five are inexpensive fixes.
What can you check before you call?
Two of these take a minute and cost nothing. Start there before booking a visit, because a technician will check them first anyway.
- Thermostat fan setting: ON runs the blower constantly, so you feel room-temperature air between heat cycles. AUTO is what you want.
- Filter: hold it to a light. If you cannot see light through it, restricted airflow is overheating the furnace and the high-limit switch is cutting the burner.
- Furnace switch and breaker: the service switch on the wall looks like a light switch and gets flipped by accident.
What are the signs it needs a technician?
If the burner lights and then goes out after a few seconds, that is usually a dirty flame sensor. The furnace is proving it cannot detect a flame and shutting the gas off on purpose. It is a safety feature working correctly, and it is a cheap clean.
A high-efficiency furnace that short cycles and blows cold may have a plugged condensate drain. Ours run wet in the Fraser Valley climate, and the safety float will stop the burner rather than let water back up.
When is cold air actually serious?
If you smell gas, leave and call the gas emergency line before anyone else. If you smell something acrid or burning, shut the furnace off at the service switch.
A furnace that runs constantly, never satisfies the thermostat, and blows air that is only slightly warm may have a failing heat exchanger or a gas supply problem. Both need a ticketed technician the same day.
No-heat calls are the bulk of our winter work across Maple Ridge, Pitt Meadows, and Mission. Most turn out to be a sensor, a filter, or a drain, and we tell you that rather than quoting a system.
Book Heating Repair
Flat diagnostic fee, and you approve the price before any repair starts.