Your boiler's main internal computer has developed a malfunction and can no longer control the heating system safely.

PCB fault

What causes this fault?

This fault occurs when the boiler's central control board suffers an internal hardware failure or a memory error, preventing it from processing safety data. The most common reasons are electrical surges, moisture ingress from a small internal leak, or simply the natural degradation of electrical components over time. Because the board can no longer communicate with the boiler's sensors, it shuts down the system entirely to prevent an unsafe operation.