Apollo Fanfare Boiler?

Same as Andy Mills. Have changed pump, overheat thermostat and fan...all work fine. Then intermittant problem where boiler cuts out after 30 to 45 mins working. Pump over-run continues but fan and ignition won't start until the system has 'rested'. Most reliably re starts after mains power has been turned off to whole system. Problem worse first thing in the morning, rather than the evening