Furnace Pilot or Ignitor Not Lighting: What to Check Safely
Last updated Reviewed by Waseem Shahzad, Lead Technician
Smell gas or hear a carbon monoxide alarm? Leave the house first, then call 911 or the gas utility from outside.
How does a gas furnace light?
Most furnaces on Long Island light in a set order: the thermostat calls, the inducer motor starts, a pressure switch proves the venting, the hot surface ignitor glows or a spark lights a pilot, the gas valve opens, the flame sensor proves the flame and the blower starts. If any step fails, the furnace stops.
Older furnaces may have a standing pilot that stays lit all the time. Newer ones use a hot surface ignitor, a small element that glows bright orange, or an intermittent pilot lit by a spark. Knowing which one you have helps you describe the problem when you call.
What can the furnace status light tell you?
Most modern furnaces have a small light on the control board, visible through a window in the lower panel. It blinks in a pattern that matches a chart on the inside of the furnace door. Count the blinks and note them before you call; it often points straight at the failed step.
Common faults the chart covers include a pressure switch that did not close, a failed ignition attempt, a lost flame signal and a high-limit trip. You can read the light without removing the panel.
What can you safely check?
Check the thermostat, the filter, the service switch and breaker, that the furnace door is seated, and on high-efficiency furnaces, that the condensate drain is not backed up. Also check that other gas appliances work. Those checks solve a good share of no-ignition calls.
- Thermostat: Set it to Heat and several degrees above room temperature; replace weak batteries.
- Filter: Replace a dirty filter; restricted airflow can trip the high-limit switch.
- Power: Check the furnace service switch and its breaker.
- Door: Make sure the blower door is fully seated; its safety switch cuts power when it is loose.
- Drain and gas: On a high-efficiency furnace, look for a backed-up condensate trap or hose. Check that the stove or water heater has gas.
- Read the light: Count the status light blinks and match them to the chart on the door.
What should you never do?
Never hold a match or lighter to the burners of a furnace with an ignitor, never bypass or jump the pressure switch or flame sensor, and never touch the ignitor; it is fragile and oils from skin shorten its life. If you smell gas, leave the house and call 911 or the gas utility from outside.
On an older furnace with a standing pilot, relight it only by following the instructions printed on the furnace exactly, and only if there is no gas smell. If the pilot will not stay lit, the thermocouple or gas valve likely needs service.
What does K2 do when a furnace will not light?
We read the fault code, then test each step of the ignition sequence: inducer, pressure switch, venting and condensate drain, ignitor, gas valve, flame sensor and control board. You get the cause and the price before the repair. Ignitors, flame sensors and pressure switches are common van parts.
In Commack, a failed control board was not powering the inducer or blower; we replaced the board and the hot surface ignitor. A yearly tune-up like this twin-furnace tune-up in Babylon cleans flame sensors before they cause lockouts. If the furnace runs but blows cold air, see furnace blowing cold air.
Common questions
Why does my furnace light and then shut off after a few seconds?
Very often a dirty flame sensor. The burner lights, the sensor cannot prove the flame, and the control shuts the gas off. Cleaning or replacing the sensor usually fixes it.
My furnace ignitor glows but the burner does not light. What does that mean?
The ignition step worked, so the problem is usually gas supply or the gas valve. Check that other gas appliances work, then call.
Is a cracked ignitor dangerous?
Not dangerous by itself, but it will stop the furnace from lighting. It is a routine replacement for a technician.
Need a technician?
Call or text us 24/7 from anywhere within 15 miles of Deer Park. You get a time window and the price before any repair.
Call 24/7: (631) 414-7141