Worceser CDi classic Return Manifest install

[Jonh57]

I just ordered a Worceser CDi classic Return Manifest/unit , part number is 87161064420.
A photo is attached of the unit upside down. What does slotted light circular piece in the centre control when turned.
You can fit a flat headed screwdriver and turn it, it arrived brand new fully turned anti-clockwise and can be turned 90 degrees clockwise.

 

[Agile]

This is the right hand return manifold1

Quite a pain to fit and probably a job many professionals would try to avoid if possible.

 

[Jonh57]

Yes, and i'm fitting it on a 2018 Worceser 29 CDi classic. The problem is Worcester have replaced this part with a newer universal one to work in more boilers.
The original version of this return manifold that is leaking on my boiler doesn't have this light circular part as shown in the above picture (that can be turned 90 degress with a flat screwdriver).
I'm unsure if this has to be open or closed. Any one know what position this has to be (turned left or right) for a CDI combi.