Glow worm Hideaway FF?

I have a Hideaway 60FF. It will always ignite when system starts in the morning but as soon as the room reaches required temperature it turns its self off as it should but then when temperature drops below that set on the controller on the wall the boiler frequently fails to restart. The pump works but no gas ignition. I have a service contract but I cannot demonstrate the fault. Engineer had not heard of that type of fault.