Your boiler has lost the connection to its internal control bridge, which is preventing it from starting up properly.

Jumper 8-9 not detected.

What causes this fault?

This fault occurs when the electrical connection that bridges the safety circuit on the boiler's control board is broken or missing. It is often caused by a loose wiring connection to your external thermostat, a damaged link plug, or a vibration-induced failure of the circuit board. Without this continuous connection, the boiler shuts down immediately as a safety precaution because it cannot confirm if external controls are allowing it to fire.