Status LED flashes 1 time repeatedly; furnace will not start heating cycle

Safety first: Turn off gas at the shutoff valve near the furnace and disconnect electrical power before removing burner compartment doors. Gas leaks and ignition issues can be hazardous.

• Check gas supply: Confirm the manual gas shutoff valve to the furnace is in line with the pipe (open). Verify other gas appliances in the home work.
• Inspect hot surface ignitor: Remove the burner access panel. Locate the ignitor (usually a ceramic element near the burners). Look for cracks or white spots. Do not touch the element with bare fingers. If cracked or open-circuit (test with ohmmeter), replace.
• Clean flame sensor: Remove the flame sensor rod (usually held by one screw). Lightly clean the metal rod with fine steel wool or emery cloth until shiny, then reinstall and reconnect the wire.
• Reset power: Restore gas and power, then call for heat at the thermostat and observe the ignition sequence through the sight glass. If the ignitor glows but burners never light, suspect gas valve or gas supply. If burners light but shut off quickly, suspect flame sensing issues.

If you smell gas or see delayed ignition (small explosion), shut everything off and contact a professional immediately.