peter attwood wrote:
Thanks for the suggestion, everything is obvious isn't it when someone tells
you. Slight problem, stopcock feeding hot water cylinder is stuck, looks
very old and not used in years. Not sure what will happen if I apply some
force to it ,to try and free it. I assume I can achieve the same by emptying
the cold water tank in the loft which feeds the cylinder, and either turn
off the mains, or tie up the ballvalve on the tank to stop it filling.

You can get rubber bungs (in t'olden days a carrot and a potato were
used) to put into the CW tank outlet and the vent pipe to seal the system.

Owain