Cheers for the replies guys, but I may have cracked it.....

found Ed Sirett's FAQ on sealed systems ans sused that last time I
pressuried the exp vessel I did so with the boiler drain valve shut. I tried
it again with the boiler drain left open (both feed and return to the rads
sealed off with the isolation valves)

Good thought there Set Square....

It seems to be bahaving better now, and the cold pressure has stabalised at
1.5 bar (thats normal for this boiler) so maybe (fingers toes etc crossed)
that sorted it. Maybe the CH fitter did the same. He did say he was not used
to this boiler or maybe he was just cr@p !

We shall see what happens over the next 24 hours, but I will check
availabilty / price tomorrow......

thanks again

Duncan