Possible Bypass Pipe problem (split off)

[Northern Guy]

I have the same system with the addition of a stop cock in the pipe in question. I'm guessing it needs to be set in a position to balance the system. Too far closed, certainly any more than half way, probably less = lots of gurgling. Fully open. Boiler starts and stops a lot and heating takes a long time to get the house warm.

 

[ianmcd]

A By-pass is there for when demand stops, and the zone valves close the boiler needs for the pump to keep running to dissipate the residual heat which over time would damage the boiler, not all boilers require a by-pass, but as you have one fitted I am guessing yours does, that is not a stop cock that is a gate valve and it is common to use a gate vave on a by-pass, it should have been set by the installer and left alone once set

 

[picasso]

Or an even better option would be an automatic bypass properly set .