"Roger Mills" wrote in message
...
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



The pressure would be the same throughout the system if the whole thing is
sealed. The pressure vessel is not actually replenishing or supplying the
system, as would happen with a normal header tank, but only compensates and
allows the system to expand and contract as needs be. The cold start
setting is only set to allow the pump to run without struggling against the
static weight of water. It helps to give it a gentle push if you like.