Your boiler's main control panel is having trouble talking to its own internal computer, meaning you cannot change settings or control the heating properly.

Control mode: Communication fault – programming unit (internal)

What causes this fault?

This fault occurs when the digital brain of the boiler loses its connection with the display screen you use to adjust settings. The most common reason is a loose internal wire or a component failure on the circuit board that prevents data from flowing between parts. It is essentially a communication breakdown inside the boiler's electronics that stops it from following your commands.