Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.

Control box failure

What causes this fault?

This fault occurs when the boiler's main electronic brain suffers an internal hardware failure, preventing it from processing instructions. It is usually caused by electrical wear and tear over time or a communication breakdown between the internal circuit boards. Because the boiler can no longer monitor safety sensors or manage the flame, it shuts down completely to prevent damage.