My in laws have a mixer shower that me and he fitted a few years ago. Their
system then was a gravity fed solid fuel system, with a copper cylinder and
a massive cold water header tank in the loft. The shower was fed from these
two tanks. They have now had the system changed to a gas combi boiler and
all is fed at mains pressure, the main reason for the change is they are
getting on a bit and the thought of having to go for the fuel at the bottom
of the garden started to look less appealing!

The problem is if anybody flushes a toilet, turns a cold tap on etc. when
the shower is in use it gets a bit hotter due to the 'now shared' cold water
pressure. It doesn't get hot enough to scald so isn't a major rproblem but
if it can be quite easily and quickly remedied the FIL would like to do it.
Due to him being nearly 70 and the bathroom looking really nice with flush
fitting shower valve and head, replacing it with a thermostitic mixer is NOT
an option.

Any ideas / thoughts most welcome.

Cheers

John