Hope someone can advise as to my next step. The initial problem was the boiler would go over pressure and blow off, hence resulting in the pressure showing <0. Called heating engineer who diagnosed a pressure release valve problem(prv) so replaced that, again, it went over pressure next statement is you need a new boiler the expansion vessel is gone. OK I accept this could be the problem but obviously wanted to be certain before I take that path as the kitchen would have to be dismantled to carry out any replacement. Asked another engineer to carry out some tests and perhaps reaffirm the initial analysis. Well he proceeded to say we should check the expansion vessel and recharge as first action, he proceeded to turn off the flow and return then drain the boiler, checked expansion vessel and recharged it to 1bar, asked to leave that way for an extended period, which we did the level on the pressure indicated on the pressure gauge dropped slightly after a period of some twenty hours. Turned on hot water after this period worked fine boiler went up to 60 degree etc. no problem, then tried the central heating having turned on the flow and return the system lasted much longer but again went over pressure and blew off. My main question is do I have to conclude that it is time to change the boiler, or should I try drawing down off a rad not being used heavily to perhaps utilise as an expansion vessel as someone suggested to again try and prove this issue. Any help on this would be sincerely appreciated