John Rumm wrote:
On 20/05/2017 17:44, ChrisK wrote:

The mains water supply pressure has no real bearing on the primary
heating side of the boiler - that is pressurised via a filling loop to
typically a bit over 1 bar. It then rises somewhat as the water heats
up. The only bit of a the boiler that will see the full mains pressure
is the secondary heat exchanger that heats the water from the primary
side of the boiler.


Of course, I knew that :-(, must engage brain before touching
keyboard... It is running at about 1.5 bar.

There is a noticable issue with HW water flow rate upstairs &
interaction between showers & filling the bath is a bit slow. This is
probably down to re-using the original 15mm pipe work. It would have
been better to have replaced this with 22mm.

Choosing pipe sizes carefully can minimise interactions a bit. Although
a 15mm pipe will likely be able to supply as much hot water as most
combis can produce. Also a smaller pipe will give you less dead leg of
water to drawer off at each use.



Agree, it's not a problem, just a noticeable side effect & the 15mm pipe
run is quite long with a lot of bends in it.

CK