Your boiler has detected an electrical problem with the system that controls the gas flow, meaning it cannot light safely for heating or hot water.

Gas–valve control – defective | Cause: Short circuit/earth (ground) leak in cable loom to gas valves, gas valve assembly defective (earth/ground leak from coils), electronic control system defective

What causes this fault?

This fault occurs when the boiler's central computer loses the ability to safely communicate with the gas valve. The most common reason is an internal electrical failure within the valve's coils or a malfunction on the main control board, which prevents the system from regulating fuel flow. In some cases, it can also be triggered by damaged internal wiring that has developed a short circuit.