Furnace will not run; LED indicates door open or no blower door switch engagement.

Safety: Always ensure the blower door is securely in place before operating the furnace.

Steps to check:

• Reinstall blower door: Align the bottom tabs and push the door firmly into place so it fully depresses the door switch.
• Inspect switch: With power off, verify the door switch actuator moves freely and that wires are securely attached.
• Test continuity: Using a multimeter, check that the switch closes (shows continuity) when pressed.

When to call a technician: If the switch is broken or the furnace still indicates an open door with the panel installed, have the switch and wiring professionally checked.