I have just replaced the ball valve on the Cold Water tank in the loft, as it was not shutting off correctly and causing large amount of overflow. I managed to replace that successfully, but now the hot water pressure is severely reduced, to the point we can't use the shower.
We believe the root cause of this is due to the entire cold water tank (and possibly the Hot water tank too) being drained whilst the water was shut off, (who would have thought a bath took so much water!).
Has anybody got any ideas about the cause and solution of the problem?