Furnace does not start; status LED shows 8 flashes repeating.

Safety: Disconnect power before servicing. Gas and combustion components must be handled carefully.

Steps:

• Verify line voltage polarity: At the furnace disconnect, confirm hot and neutral are correctly wired. Reversed polarity can weaken flame sensing. This check should be done by someone comfortable with electrical testing.
• Clean flame sensor: Remove and clean the flame sensor rod thoroughly. Reinstall and ensure the wire connection is tight.
• Clean burners: Remove the burner assembly if accessible. Brush off rust and debris, and clear any blocked burner ports with a soft brush or compressed air. Reinstall burners correctly aligned.
• Check ground: Ensure the furnace cabinet is bonded to ground and that the control board ground lug is secure.

Note: If the flame signal (measured in microamps by a technician) remains low after cleaning and grounding corrections, the control board may need replacement.