Heater shows F12 and will not start; may occur after a power surge or lightning event.

Safety first: Turn off power at the breaker before inspecting the control board.

• Power cycle: Turn off power to the heater for at least 5 minutes, then restore power and see if F12 clears. This can reset minor logic faults.
• Inspect board visually: Remove the control panel cover and look for burned spots, bulging capacitors, or melted traces on the Thermeau control board.
• Check incoming power: Verify that supply voltage matches the heater’s rating and that neutral/ground connections are secure.
• Surge protection: If F12 followed a storm or outage, consider adding an external surge protector to protect the replacement board.
• Replace board: If visible damage is present or F12 persists after power cycling, replace the main control board with the exact Thermeau replacement part.