Your boiler has stopped working because its internal pressure sensors have been plugged into the wrong sockets during a service or repair.

High Pressure Sensor and Low Pressure Sensor Wiring-Cross-Connection

What causes this fault?

This fault occurs when the electrical wires for the boiler's internal high and low pressure sensors have been swapped or plugged into the wrong ports on the control board. It typically happens during a recent repair or service where the technician accidentally switched these identical-looking connections, leading the boiler to receive incorrect safety information. Because the system can no longer accurately monitor water pressure, it shuts down immediately as a safety precaution.