Glowworm back boiler & open fire Problems with lighting & Dust?

We have had our glowworm inset bbu50 open fire and back boiler for 7 years. We have had numerous problems, 2 new circuit boards, new fire front, new thermostat, and servicing at least twice a year to keep it working.

Last christmas our thermostat blew and this had all the pipes, radiators, and water tanks shaking. If we had not been in the house, i dont know what would have happened as it didnt cut out. Since fitting the new thermostat, when the heating is on, its on for a minute, off for a minute, and this is how it goes continously. Even on minimum the radiators are very hot, anything over minimum and the boiler is very noisy (bubbling).

We last had our boiler serviced in mid sept 06 and now mid jan 07 its tripping out again. This is normally as its a little dusty - even though this gets clean every other week, but at the moment when the boiler lights is theres a big loud flash often comes out of the fire front.

Is there any thing you can suggest our service engineer check as he is calling on monday or any ideas how to make this system more efficient?

Is there any know problems with this back boiler?