Code 12, blower runs after heat cycle much longer than normal, occasional limit trips

Safety first: Turn off power before accessing the control board.

• Step 1 – Allow cool-down: After a power interruption, the board may run the blower to cool the heat exchanger. Let the furnace run through a full cycle and see if behavior normalizes.
• Step 2 – Check filter and airflow: Ensure the filter is clean and registers are open to prevent overheating that can extend blower run time.
• Step 3 – Inspect board settings: Some Ducane boards have dip switches for fan-off delay. Verify they are set per the installation manual.
• Step 4 – If blower never shuts off: See the E7 scenario for diagnosing a stuck fan relay or miswired G circuit.