How can we fix the rattling in our Ferroli boiler?

A couple of weeks ago our Ferroli Boiler wouldn't go on. An engineer came and said it was the starter switch and put in a new one. Since that time it has started but with a slight rattle which we thought was because the switch had to settle down. Unfortunately the noise has got a lot lot worse. We are unable to get hold of the original engineer and another one we had seemed to think it would cost nearly £200 to put right but we think that maybe it is because the switch hasn't been put in correctly. We don't want to be ripped off and pay this money especially before Xmas if it is just the switch. Has anyone else had this problem?