I've just refitted my Ravenheat LS100 combi after removing it so I could replaster the room. Now when it fires up, unless it's on very low heat. The burner lights, recycles twice then the overheat stat trips. I've noticed the ignition is sparking continuously throughout this time. Anybody got any suggestions before I call out an engineer. PS The boiler is just over 15 months old and was working fine before this.