Furnace inducer starts but burners never light; LED shows 1 flash on York control board.

Safety first: Turn off power at the furnace switch and shut off gas at the gas cock before removing panels. If you smell gas continuously, evacuate and call the gas utility or a licensed technician.

• Check gas supply: Verify the manual gas shutoff valve to the furnace is parallel with the pipe (open). Confirm other gas appliances work.
• Inspect hot surface ignitor (HSI): Remove the burner access panel. Locate the ignitor near the burners. Look for cracks or white spots on the ceramic. If damaged, replace the ignitor with a York-compatible hot surface ignitor rated for your model.
• Clean flame sensor: Locate the flame sensor rod on the opposite side of the burner from the ignitor. Remove the mounting screw, pull the rod, and gently clean it with fine steel wool or emery cloth until shiny. Reinstall firmly.
• Reset power: Restore power and call for heat at the thermostat. Watch the ignition sequence: inducer → ignitor glow → gas valve click → flame. If ignitor glows but no flame, suspect gas valve or gas supply. If no glow, suspect ignitor or control board output.
• When to call a pro: If you have confirmed gas supply and a good ignitor but still no flame, the gas valve or control board may be faulty. These require manometer testing and should be handled by a licensed HVAC technician.