Status LED flashes code 42 (four short, two long). Inducer or blower may run unexpectedly; furnace may not heat properly.

Safety first: Turn off power at the breaker before checking line voltage wiring. Incorrect wiring can cause shock or equipment damage.

• Verify line polarity: At the furnace junction box, confirm that the hot (black) wire is on L, neutral (white) on N, and ground (green/bare) on ground screw. Correct any miswiring.
• Inspect ground connections: Ensure the furnace cabinet is bonded to ground and that the control board ground lug is tight.
• Check inducer operation: On a call for heat, the inducer should start first. If it hums or fails to start, test for 120 VAC at the inducer leads. Replace the inducer motor assembly if voltage is present but motor does not run.
• Observe blower behavior: If the blower runs continuously or at odd times, the fan relay on the control board may be stuck. Inspect the board for damage and replace if necessary.