Furnace will not start; status LED shows 1 red flash repeating; inducer and blower do not run.

Safety first: Turn off electrical power to the furnace at the service switch and shut off the gas at the manual gas shutoff valve before removing panels. If you ever smell gas strongly, evacuate and contact your gas utility or a licensed technician immediately.

Steps to check:

• Verify thermostat call for heat: Set thermostat to HEAT and raise the setpoint 5°F above room temperature. Confirm 24 VAC between R and W at the furnace control board.
• Check gas supply: Ensure the manual gas shutoff valve near the furnace is parallel to the pipe (open). Confirm other gas appliances in the home operate normally.
• Inspect hot surface ignitor (HSI): Remove burner access panel. Locate the ignitor on the burner assembly. Look for cracks, white spots, or breaks in the element. If damaged, replace the ignitor with a Coleman-compatible hot surface ignitor of the same style and resistance rating. Do not touch the new ignitor element with bare fingers.
• Clean or test flame sensor: Locate the flame sensor rod near the burner flame. Remove the mounting screw and gently clean the rod with fine steel wool or emery cloth until shiny. Reinstall and ensure the sensor is in the flame path.
• Check gas valve operation: With power restored and a call for heat, listen for the gas valve click after the inducer runs and ignitor glows. If the ignitor glows but there is no flame and no gas odor, the gas valve may be faulty or not receiving 24 VAC from the control board. This test should be done by a qualified technician with a multimeter.

If the furnace repeatedly attempts ignition and locks out again, contact a licensed HVAC technician to test gas pressure, combustion, and the control board.