Furnace runs but produces no heat; blower runs continuously with room temperature air.

Critical safety: If you smell gas, shut off the gas supply, evacuate, and contact your gas utility.

• Thermostat check: Ensure thermostat is set to HEAT and temperature is above room level.
• Verify gas valve position: Locate the manual gas shutoff near the furnace and ensure it is parallel to the pipe (open).
• Observe ignition: Through the sight glass, watch for ignitor glow and burner flame when there is a call for heat. No glow suggests ignitor failure; glow with no flame suggests gas supply or valve issue.
• Inspect ignitor: With power OFF, inspect the ignitor for cracks or damage and replace if necessary.

If the ignitor works but burners never light, gas pressure and valve operation must be checked by a licensed technician.