"orbis" wrote in message
oups.com...
If only! Annoyingly there are no isolator valves on the supply to the
bath taps (and therefore the shower mixer). I think this may be against
the regs, but that's a problem for another day...

I had to completely turn off the water to work on the shower.


If the water was off and drained, then has something jammed in the cold
water outlet from the water tank? Did you wrap PTFE tape or joint compound
around any fitting when re-installing the mixer valve? Is the hot water
supplied from a different source than the cold, or are they both supplied
from a storage tanks?

The only other thing I can think of, is that you have turned the hot water
supply on, more than it was before. Like hot water from a combi-boiler
supplied from the mains, and the cold supply from a tank in the loft. The
hot water will be reaching the mixer at a higher pressure than the cold
water unless a regulator (gate) valve is in the line somewhere. This
regulator valve may need resetting.