Heating valve what it does

[Mick67]

Can someone tell me what this stop valve does.
if it’s to regerlate flow how it need to be adjusted.
thanks

 

[ShaunCorbs]

Bypass valve as you have a 3 port that red valve should be shut

 

[Mick67]

It’s been partly open ,
by pass for what please

 

[ShaunCorbs]

For a boiler with a pump overrun and an s plan system, once the boiler has turned off the pump will still run for around 5 mins to dissipate the heat