What is the purpose of this pipe?

[tsp0403]

Hi Everyone,

Can anyone tell me what the pipe (with the blue isolator) is in between the pump and the motorised ch/hw valve? And should it be open or closed?

Recently had to isolate and drain the central heating system to replace some pipe work, turned everything back on, bled, balanced and refilled the system and all working fine but I seem to remember this blue isolating valve was turned off before it was all done but I can’t be sure.

I can trace the pipe to find out where it connects.

 

[Deleted member 120897]

Looks like it could be a manual bypass. If it connects to the heating return, then I’d say that’s what it is. If it is, it probably needs to be nearly closed.