Miller furnace status LED is on solid with no flashing, but the furnace does not operate correctly.

Safety: Turn off power before working on low-voltage wiring to avoid shorting the control board.

• Check thermostat: Ensure the thermostat is set to HEAT and the setpoint is above room temperature. Replace batteries if applicable.
• Verify call for heat at furnace: Remove the blower door and locate the control board. With power off, inspect the R and W thermostat wires for breaks or loose connections. With power on, you can temporarily jumper R to W at the board to see if the furnace starts. Remove the jumper after testing.
• Inspect low-voltage fuse: Many Miller boards have a 3–5A automotive-style fuse. If blown, replace with the same rating and look for shorts in thermostat wiring or accessories.
• Check door switch: Ensure the blower door is properly installed and depressing the door safety switch; otherwise the furnace will not run.