It occurred to me to wonder to what extent the recommended cold charge
pressure for a sealed system depends on the position of the pressure vessel
and gauge.

I have seen lots of suggestions saying that the easiest way to convert an
existing vented system is to replace the F&E tank in the attic with a
pressure vessel in the same position.

However, many systems (particularly if using a system boiler) with have the
pressure vessel and gauge quite close to floor level on the ground floor. In
an average house, this represents a difference of about half a bar of static
pressure between these two positions. If the gauge is in the attic, do you
pressurise to half a bar less than if it were at ground level?

Roger