Your boiler's electronic brain has developed a software or hardware error and can no longer control the heating and hot water safely.

There is an internal fault in the Automatic Control Module.

What causes this fault?

This fault occurs when the boiler's main control board suffers an internal hardware failure or a memory error in its programming. It most commonly happens due to electrical wear over time, but can also be triggered by a sudden power surge or dampness affecting the circuitry.