If you smell gas, leave the house first. Do not flip light switches or touch the thermostat. From outside, call your gas company's emergency line or 911. Call us after the gas company has made the house safe.
What usually fails
A modern gas furnace lights in a set order. The inducer motor clears the flue, a pressure switch confirms the draft, the hot surface igniter glows, the gas valve opens and a flame sensor confirms the burners lit. A failure at any step shuts the furnace down. Many furnaces flash an error code on a small light behind the lower panel, and the code tells the tech where the sequence stopped.
The flame sensor fails often. A thin layer of residue builds up on it, the furnace cannot confirm the flame, and it shuts the gas off after a few seconds. After several retries, the furnace locks out. Cleaning the sensor takes a tech about 15 minutes. Cracked igniters and failed inducer motors come up often on furnaces more than 10 years old.
Signs you need a repair
- The burners light, then shut off within ten seconds, over and over
- The blower runs but the air stays cold
- No sound at all from the furnace when the thermostat calls for heat
- A yellow or flickering flame where it should be steady blue
- A carbon monoxide alarm goes off (leave the house and call 911)
- Rumbling or a loud bang when the burners light
Typical costs
| Repair | Typical price |
|---|---|
| Diagnostic visit | $89 to $150 |
| Flame sensor cleaning or replacement | $100 to $250 |
| Hot surface igniter | $150 to $400 |
| Gas valve | $350 to $900 |
| Control board | $400 to $900 |
| Inducer motor | $450 to $1,200 |
| New gas furnace, installed | $3,500 to $7,500 |
Repair or replace?
Furnaces outlast heat pumps, often reaching 20 years, because they run only in winter. The case for replacing usually comes from a cracked heat exchanger, which can leak carbon monoxide and is not a safe repair on most units, or from a furnace old enough that parts are hard to find. If the AC paired with your furnace also needs work, ask for a price on both together, since replacing them at once avoids paying for a second installation.
Questions
Why does my furnace start and then shut off?
A dirty flame sensor is the first thing a tech checks on a furnace that lights and then quits. A clogged filter that overheats the furnace and trips the high-limit switch is next.
Is it safe to reset my furnace?
Turning the power switch off and on once is fine. If the furnace locks out again, leave it off and call. Repeated resets on a furnace with a draft or gas valve problem can be dangerous.
Do you cover propane furnaces?
Yes. Many homes in rural Chatham and Orange counties run on propane, and Our technicians handle propane and natural gas units.