Your boiler's internal computer has lost its connection to its main controls, meaning it cannot receive the instructions it needs to provide heating or hot water.

No BUS communication cable, EMS-Bus isn’t connected or damaged – connect the cable for the EMS-Bus or replace the damaged cable exchange fuse

What causes this fault?

This fault occurs when the boiler's central computer loses its physical connection to the internal wiring system that carries data commands. It is usually caused by a loose connection, a broken wire, or a blown fuse on the circuit board that prevents signals from reaching the vital components. Without this communication link, the boiler cannot receive instructions to fire up, even if the rest of the hardware is functioning correctly.