Question details (performance):
The boiler is overheating in operation.
Answer: Fault reason:
1. High cycle resistance of the system (blocked).
2. The overheating sensor is defective or disconnected.
3. Water pump does not circulate or impeller is plugged.
1. Confirm pipe and valve are reliable.
2. Confirm point of discharge and adjust or replace igniter.
3. Replace the main controller.