The short answer
Run the heat for a few minutes on a mild fall day, change the filter, and test the carbon monoxide alarms before you need any of it. Furnaces here sit idle for months, so the first cold night is when faults surface — and finding them in October is cheaper than at 2 a.m.
Why do furnaces fail on the first cold night?
Coastal Georgia does not ask much of a furnace, and that is exactly the problem. Equipment that runs a handful of weeks a year sits idle for months, and the first genuinely cold night is when everyone finds out what did not survive the summer.
What should you check yourself before winter?
- Change the filter
- Replace the thermostat batteries and set it to heat
- On a mild day, run the heat for a few minutes and listen
- Check that the breaker is on and the furnace door is closed — the door switch stops it running otherwise
- Make sure the gas supply is on
- On a high-efficiency furnace, check the plastic vent pipes outside are clear
- Test the carbon monoxide alarms, and fit them if there are none
A brief burning smell the first time the heat comes on is normal — it is dust burning off. A smell that persists is not.
What usually fails after a summer idle?
On modern furnaces the usual suspects are the igniter and the flame sensor. A hot surface igniter is a consumable: it degrades with every cycle and eventually cracks. A flame sensor does not fail so much as foul — a thin film builds up, the furnace lights, fails to confirm the flame, and shuts down within seconds. That pattern, lighting then dropping out almost immediately, is close to diagnostic on its own.
A furnace that runs but cuts out after several minutes points somewhere else, usually a limit switch responding to a genuine overheat. The cause is often airflow — a filter left in too long, a closed-off return, a failing blower. The switch is doing its job, and replacing it without fixing the airflow just removes the protection.
Which warning signs mean stop and call?
- Repeated short cycling
- Soot around the furnace or its vents
- A burner flame that lifts, rolls or burns yellow
- A carbon monoxide alarm — get everyone outside, then call 911
- A smell of gas — leave the house and call the gas utility from outside
What does a professional heating check cover?
ENERGY STAR's checklist for a heating visit includes the gas connections, gas pressure, burner combustion and the heat exchanger, along with the electrical connections and controls. The heat exchanger inspection matters most: a cracked one can put combustion products into the air you breathe.
A furnace tune-up starts at $129. If the parts that usually fail have to be replaced, a flame sensor starts at $149 and an ignitor at $199.
Also asked.
- Is a burning smell normal when the heat first comes on?
- A brief one, yes — it is dust burning off the heat exchanger after months idle. A smell that lasts, smoke, or the smell of gas is not normal: switch the system off and call.
- How often should a gas furnace be serviced?
- Once a year, in the fall, before the heating season. ENERGY STAR recommends a pre-season heating check that includes the gas connections, burner combustion and heat exchanger.
Sources
- ↗Maintenance Checklist — ENERGY STAR (U.S. EPA)
- ↗Carbon Monoxide Information Center — U.S. Consumer Product Safety Commission