Ok - so I have tried that - put them on the shower and the bath - but no change. still the same problem. when I isolate the cold feed to the boiler and turn on the hot - there is still cold water coming out of the taps - does this just mean that I have to put them on ALL of the taps in the house?
I know - and I really appreciate the help - I am just so fed up with people coming around to my house and not fixing it and then charging me for "work carried out". sorry. and thanks again.
Pixie dust I think. Ok - point taken. So it would seem that I, yet again, have to come along behind a "professional" tradesman and sort out poor (and expensive) "workmanship"
ok... - but it is happening on all of the taps in the house - or will putting them on the bath supplies solve the rest of it as well? (thanks for your help btw - (y))