have a problem with my boiler its a ferolli falcon when i put the central heating or the hot water tap on i get nothing happening at the boiler, the boiler does have a reset switch and when i switch that the boiler will fire up showing the light of c.h and will fire up for bout 5 seconds and then cut off, the light will remain on and at random times the boiler will fire up again for 5 seconds again. ive had a engineer out 2day and he cant figure whats wrongs his done a diagnostic but say that it is loads of things that has gone but he believe that it cant be the case, then he said its the pcb. now when was testing thing he pulled the high limit thermostat out out and the boiler run fine but when in it cut off.so he said that cud be the problem, now when he left my dad had a mess around and the c.h and water started working fine, we had the heating running for an hour then we switched it off, now 2 hours later we tried it again and now its back to not working any ideas what it cud be.