Dettson furnace displays E7 and will not start a heating cycle; no inducer or blower operation.

Safety first: Turn off power at the breaker before accessing the control compartment.

• 1. Inspect control board connections: Remove the blower door and locate the main control board. Check all plug-in harnesses for secure seating. Gently press each connector to ensure it is fully engaged.
• 2. Look for visible damage: Examine the board for burnt spots, cracked solder joints, or swollen components. Any visible damage indicates the board should be replaced.
• 3. Verify correct line voltage: Confirm that the furnace is receiving the correct supply voltage (typically 120 VAC in North America). Overvoltage or miswired power can damage the board and must be corrected by an electrician.
• 4. Power cycle: Restore power, wait 30 seconds, then turn the thermostat to call for heat. If E7 reappears immediately and all wiring is correct, the control board is likely defective.
• 5. Replace control board: Label all wires, take a photo, then remove and replace the board with the exact Dettson replacement. Transfer one connector at a time to avoid miswiring. This task is best handled by an experienced DIYer or technician.