On Sat, 10 Feb 2018 18:17:08 +0000, Pinnerite wrote:

A British Gas salesman ...

Run, don't walk, away.

Ask around for a local tradesman and see if a name or two repeatedly
get positive recomendations (or negative...)

tested the cold water pressure (it looked pretty fierce to me) and said,
"you cannot have a Combi. Pressures too low".

Others have suggested doing your own flow and pressure tests, if the
pressure really is high you can get PRV's (Pressure Reducing Valves).
I think they limit both the static and dynamic pressures.

Presumably the boiler change is to free up a bit of space by getting
rid of the HW cylinder and header tank? Otherwise doesn't "if it
ain't broke, don't fix it" apply?

--
Cheers
Dave.