Your boiler's internal computer has encountered a critical error and can no longer control the heating and hot water functions 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 experiences a hardware failure or a memory error, meaning it can no longer process data correctly. The most common reason is natural wear and tear of the electronic components, though electrical surges or moisture getting onto the board can also trigger this complete failure.