I need to turn off the hot water to fix a tap, but I just can't turn the
stop tap. This is on a pipe behind the hot water cylinder running up to the
loft and it's got a flat oval shaped piece to turn. I've found it tight in
the past and have use mole grips, but this time I can't budge it.

Am I likely to damage anything if I really get brutal, or is there any way
of freeing it up? Alternatively, I presume I can turn off the cold water
feed to the house and drain the tanks. (In the long term, I think I'm going
to have to replace this tap.)

Peter.