STOP
You've done far more to your boiler than you're legally allowed to do, and you may be putting yourself and your family at considerable risk of death. You need to call a boiler engineer to sort your problem, which could be any of a number of things
He can do whatever he likes in his own house legally.As long as he feels he is competent to do so.
Lay off the 'fear factor' Muggy.
Too many of you plumbers' like to get your easy work off fear factor .
If plumbers were reasonable people- many more customers would come their way .
Completely and utterly wrong PP it doesnt matter in any way what so ever what the person feels competent to do he has to prove competency hence ACS if he holds ACS with the appropriate elements then he may work on his own appliances without being Gas Safe registered but not if he rents out any part of his home