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Furnace Won't Stay Lit

Burners that light then go out within seconds usually mean a dirty flame sensor or weak gas pressure. Flame sensor cleaning is a common fix — $100 to $300 professionally.

Reviewed July 2026

What does furnace won't stay lit mean?

If you see the burners ignite but the flame dies within a few seconds, the control board is shutting off gas because it doesn't detect a stable flame. A coated flame sensor rod is the most frequent cause on modern furnaces.

What usually causes furnace won't stay lit?

Dirty flame sensormost common

Typical repair: $100–$300

Weak or failing ignitorcommon

Typical repair: $150–$400

Gas pressure or valve issuepossible

Typical repair: $350–$900

Find your exact error code

Select your furnace brand to jump to the code page for this symptom.

DaikinE6Low flame-sensor signalTempstar6 FlashIgnition or flame-sense failureHeil6 FlashIgnition or flame-sense failureComfortmaker6 FlashIgnition or flame-sense failure

What should I check first when furnace won't stay lit?

  1. Watch one full ignition cycle — note if flame appears then disappears.
  2. Check that the gas valve is fully open.
  3. Replace the air filter; poor airflow can cause flame rollout.
  4. Do not disassemble the gas valve yourself — call a licensed tech.

What a repair costs

A flame sensor cleaning or replacement typically costs between $100 and $300 nationally.

Typical repair cost
$100 – $300flame sensor cleaning or replacement
Where the money goes
Part $15–$75Labor $25–$285Typical labor time: 0.5 hrs

This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.