Your boiler has started up but could not detect a flame, so it has stopped as a safety precaution and will likely need a reset and a check of the burner's sensor and the air supply.

Burner in a fault state. Flame signal is not present or insufficient at burner start. Check ionisation electrode and connecting cable. Check plug-in connections for loose contacts. Note: Deposits on the electrodes indicate foreign bodies in the combustion air. Check the installation room and flue system for causes of the deposits. Reset device.