Can you please advise me:

addisb

Attached photo of the plumbing system in my hot press. The pipe and valve arrowed. What exactly is this particular pipes function. With the heating up and running ( which it is not ) should this valve be open or closed ?
Thanks a million in advance for reply.

K.Flyer

It appears to be a by-pass pipe.
The valve would normally be barely open, a half turn open at most.
Better to have an automatic bypass valve fitted.

addisb

Thank you for reply K.Flyer .if I may query further.. what by-passes what ? What is its purpose ?

K.Flyer

In the event of the thermostic valve on your hot water heating circuit closing and all of your radiators being off at the same time, it allows a minimum flow of water to circulate through the main heating pipework so that your circulation pump is not pumping against a closed pipe, which could cause damage to the pump.
If it is left open too much, then the flow of water will follow the path of least resistance, causing the radiators, and to a lesser degree the hot water, to heat up much slower.
An auto by pass keeps that section closed and will only open if required.