Your boiler's internal computer has encountered a critical error and cannot safely operate the system.

Control box errors - possible faulty control box.

What causes this fault?

This fault occurs when the boiler's internal computer brain fails to communicate correctly with the safety sensors and ignition components. It is physically caused by a microchip failure or a corrupted circuit on the main control board, preventing the boiler from managing the heating process safely. The most common reason is general electronic wear and tear or a power surge that has damaged the delicate internal wiring.