On an aside, I was thinking of using the pipe freezer once - until I saw the
cost in B&Q - one can at some hideous price to do one pipe for one session.

That made me go and seek out all the valves and check them before I started.
As it happened, the right valves worked so I didn't need to freeze stuff.

As I rebuild the system, I'm going to make sure that I include decent
quality ball valves at strategic points and turn them once a year.

A plumber doing this would possibly have a "proper" freezing kit which is
more like a mini fridge compressor with a clamp on cooling doobrey which
makes the running cost smaller (ie can be used again and again).

The canned stuff is probably useful if there is no other way, but it's not
cheap enough to make it a no brainer IMHO.

Cheers

Tim