Your boiler is failing to light the flame needed to produce heat and hot water, likely due to a combustion issue.

Technical description

Ignition problems / If the air-gas mix ratio is incorrect then this will prevent combustion and can force the boiler into a state of lockout. Technical Note: if the Flame Control Unit is not detecting a flame it could be due to one of the following reasons: the flame has not ignited; the flame control unit has become disconnected from the burner.