Your boiler's internal computer brain has experienced 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 internal computer experiences a catastrophic electronic failure, preventing it from processing safety information or managing the burner. The most common reason is the natural degradation of electrical components on the circuit board, which can sometimes be accelerated by power surges or moisture ingress. Because the brain of the boiler is no longer functioning correctly, it shuts down the system entirely to ensure your home remains safe.