RobertL wrote:

That's what I suspect also, especially as it gave an OK result at
first and then started to drop. However, his first port of call is to
disconnect the parts of the pipework that lead to terminations that
don't have appliances on them.

We are getting the original plumber aback who did the previous test
(and some pipe works).

Thanks for your guidance people.

If you bought your own manometer (B&Q sell them) you could rule out leaks at
the nipple. If it turned out to be that then you could probably ask for a
retest.

Tim