Furnace will not start; Miller control board LED flashes 6 times repeatedly.

Critical safety warning: An open rollout switch indicates flames or excessive heat left the burner area. Turn off gas and power and do not attempt to repeatedly reset the switch without finding the cause. Carbon monoxide risk is serious.

• Locate rollout switches: These are small, manual-reset temperature switches near the burners. Check if the red reset button (if present) has popped. Do not reset until inspection is complete.
• Inspect burners and orifices: Remove burners and check for rust, debris, or misalignment. Clean with a soft brush and compressed air. Ensure orifices are not plugged.
• Check vent and heat exchanger: Inspect the flue pipe for blockages or disconnections. Look for signs of rust-through or cracks in the heat exchanger. If a cracked heat exchanger is suspected, shut the furnace down and contact a licensed HVAC technician; the heat exchanger or furnace must be replaced.
• Reset and test: After correcting any obvious issues, press the rollout switch reset (if applicable), restore power and gas, and observe operation. If the rollout trips again, shut down and have the system professionally evaluated.