"Peter Hemmings"wrote

snip

The reason I was not going to shut all valves was that I have 2 towel rads
which are never shut/adjusted so I thought I would never get to the state
when everything was shut!

Don't you have a zone valve controlling all flow to the central heating, or
is this Baxi Barcelona supplying one heating circuit only and no h/w?
If it has a zone valve upstream of the towel rads then the by-pass will be
needed of course.

Phil