Ignitor glows but burners do not light

What is going on

Inducer runs, the ignitor heats up and glows, and then no flame. What I usually find is gas pressure that is out of range, a loose plug on the gas valve, or a valve that never got its 24 volts. Start by working out whether gas is reaching the burners and whether the valve is being told to open. Gas work is for a qualified gas technician, so if you are not one, stop at the voltage checks.

Likely causes

• No gas or line pressure out of range
• Gas valve or plug wiring miswired or loose
• Gas valve failed
• Control not supplying 24 V

Check in this order

1. Gas work qualified gas tech only
2. Check line pressure at the valve. It should stay at or below 13 in. WC. Minimum is 4.5 in. WC natural gas and 8.0 in. WC propane
3. Check the gas valve wiring and the multi-pin plugs for loose connections
4. About 35 seconds after the heat call, check for 24 V at the valve
5. Replace the valve if 24 V is present and it does not open
6. Replace the control if there is no 24 V
7. Confirm the manual shutoff is open and the tank has fuel if on propane
8. Check for gas leaks with approved detector after any work

More furnace guides

• AM radio static during ignition
• Blower motor does not run - Lennox SL280UHV ECM checks
• Burners light, then the furnace shuts down early
• Display shows two horizontal bars (soft disable) - Lennox SL297NV
• EL296UHV: normal gas heat sequence (what should happen after a call for heat)
• EL296UHV: what the display and the diagnostic button are telling you