Your boiler is failing to detect the flame because the internal sensors that manage the ignition process are disconnected or experiencing a wiring fault.

Fault: Electrodes. Electrodes not connected or they are connected incorrectly, short circuit in the cable harness

What causes this fault?

This fault occurs when the boiler's control board loses communication with the components responsible for creating the spark and sensing the flame. It is usually caused by a loose connection, damaged wiring, or electrodes that have worn down and can no longer complete the electrical circuit required to start the boiler. Without this secure connection, the system shuts down as a safety precaution to prevent unburnt gas from entering the combustion chamber.