Your boiler has experienced an internal electrical communication error, which means the main control box cannot talk to the internal components correctly.

Internal error – electrical connector contacts or programmer interface module – check ignition leads are not loose.

What causes this fault?

This fault occurs when the boiler's main control board loses the ability to send or receive data from its internal operating modules. It is typically caused by a loose electrical connection, worn out ignition leads, or a mechanical failure within the 'brain' of the unit that prevents it from coordinating the heating process safely.