Your boiler has detected that it got too hot and has automatically shut itself down to prevent damage or fire risk.

The appliance will enter a lockout condition in the event of overheating. An overheat cut-off thermostat is fitted to the appliance which will interrupt the electricity supply to the ignition circuit. If the overheat cut-off has operated the fan and/or pump will run but the burner will not light. (No spark generation).