thanks Tony, yes we've tried all these place, at the bottom of the casing where there are two scews I opened that and there is some sort of valve type there, the clicking of a pump seems to be around the boiler, as for BG they charged £ 187.92 for a call out, 40 mins where the enigneer just talked through what the problem was and said that a system flush would sort it, while a system flush may provide future efficiency I think it is the theromsotat overheat that costs about £ 16 for the part on the net, as for the ststem flush they are quoting £ 500 plus VAT.
Eunan C, January 2009