LED flashes code 42; blower may not start or may run at wrong times.

Safety: Turn off power before accessing the control board. Do not attempt to repair the board at component level.

Steps:

• Inspect control board: Look for burn marks, melted areas, or a relay that appears overheated on the HK42FZ or similar board.
• Check motor amp draw: With a clamp meter (if available), measure blower or inducer current draw and compare to the motor nameplate rating. Excessive draw can damage relays.
• Check wiring: Ensure blower and inducer wires are correctly connected to the board terminals and not shorted to ground.
• Power cycle: Turn power off for 5 minutes, then restore and observe if code 42 returns immediately or only during operation.

When to call a technician: Relay or board replacement should be done by a professional, especially if motor overcurrent or wiring issues are involved.