BigWallop wrote:

NO !!!! Whoa up there Glen.

Heh, this was going to be a weekend project, so you've stopped me in time

Trace the pipework back to the pump or the tanks from which they're
supplied. Somewhere along these pipes should be taps, stopcocks or things
called Service Valves. A service valve looks just like a straight plumbing
connector, but it has a small slot cut into the middle of it. The slot
actually takes a screwdriver and is used to turn the water off to the rest
of the system so it can be serviced or repaired. Hence the name Service
Valve.

I'm familiar with what you're talking about - there are some of them elsewhere
in the house. I'm not sure where the ones controlling the shower feeds are -
I'll have to do some detective work. I know the pipes run from the attic down to
the airing cupboard in the bathroom where the hot water storage tank is, then
under the bath and up the wall to the shower (they're embedded in the wall and
tiled over).
There should be a tap on each side of the supply system, one for the hot,
and of course, one for the cold. The cold water is now coming into the
house much colder than it has been over the summer months, so the shower is
more likely struggling to keep itself hot with a much colder water supply.
If you turn the cold water supply pressure off a bit, then the shower will
not be taking in as much cold and should then be able to balance the
temperature again. So, you should get a hotter shower again.

Start looking along the pipework and try to find a tap, stopcock or a
service valve on the cold water supply side. When you find it, turn it off
a bit, not to much, until you can feel the shower getting hotter. This
might be best done with two people, especially if the pipes are in an
awkward spot, one to feel the shower temperature, while you slowly turn the
cold supply down until you're shouted at.

Thanks for the clear advice - I'll have a go at the weekend and let y'all know
how I get on.

Cheers

Glenn.