"Peter Hemmings" wrote in message
. uk...


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!

If that is the case you don't need a bypass.

Mine frequently has all the valves closed as it is controlled by 5 two port
valves that shut whenever nothing wants heat, a bypass is essential then.