Your boiler has stopped working because it cannot light the internal flame or detect that it is staying lit, so it has shut down for safety.

Technical description

Lock out/flame failure: When the ionisation electrode (28) does not detect flame presence. If a flame is not detected before 8 seconds, the grey security solenoid (30) and the blue 1/3 solenoid (31) will close. The lock out red indicator (22) lights.