Furnace will not ignite; Miller control board LED flashes 3 times in a repeating pattern.

Safety: Shut off power before working inside the furnace. Do not operate the furnace with the venting disconnected.

• Check inducer operation: Restore power and call for heat. Observe whether the inducer motor starts. If it hums but does not spin, or does nothing, turn power off and test for 120V at the inducer leads during a call for heat. If voltage is present but the motor does not run, replace the inducer draft motor assembly.
• Inspect venting: Go outside and verify the exhaust and intake (if applicable) terminations are not blocked by leaves, snow, nests, or debris. Clear any obstructions and ensure proper clearances.
• Check pressure tubing and ports: Remove the tubing from the inducer and pressure switch. Inspect for cracks, splits, or moisture. Clean the inducer port with a small drill bit or wire (do not enlarge the hole) to remove rust or debris. Reattach tubing securely.
• Test the pressure switch: With a manometer if available, verify the switch closes at the specified negative pressure listed on the switch label. If it fails to close even with proper inducer operation and clear venting, replace the pressure switch with the correct Miller-rated part.