In message , Pete C burbled:

The hot water pressure will be governed by the level in the cold water
tank the hot tank is fed from, which should be a bit higher up in the
attic.

Unfortunately, the cold water doesn't come from the attic but a small header
tank on top of the hot water tank itself, which is fed from the mains. Thus
the head of water for the hot water is near ceiling level on our
single-level flat. Cold water for all taps seems to come straight from the
mains

Another potential problem is there may be strainers on the inlet to
the venturi shower that have been blocked with dislodged scale. If the
shower hose itself is quite narrow, or there is any scale blocking the
shower head that won't help either.

I'll check to see if there's any scale near the shower, but I think the
plumber did that the last time he spent ages looking for a problem.

I've installed an old-style thermostat my (electrician) father gave me at
the weekend. It has a temperature scale on the dial from 50 to 85 degrees
(rather than the lame + and - on the new ones). I set that last night and
this morning's water is 62°C versus 56°C the other day with the +/-
thermostat. As such the shower was decently hot with the dial on 3/4 of the
way round. So we're in a more sensible place for when the incoming cold
water starts to cool down in the autumn (i.e. there's adjustment on the
shower temperature now) and I might even up the stat a little more. the hot
water from the taps feels much more like it used to - unpleasantly hot
rather than the recent bearably-hot stuff we've had. I know there are
issues with having scalding water, but we've had that for the last 8 montsh
and we're happy with it

So it looks like it was a simple case of the new stats being colder than old
style ones. i now have a small stash of old style ones in case they ever
fail


--
Ian Cowley
Bishop's Stortford/Cambridge, UK

www.iancowley.co.uk/contact