If you mean the flow from the cwsc then it should connect to the bottom of the cylinder, to create push for the hot water draw off at top, the other holes will be direct flow and return to and from boiler.
There’s a connection for secondary return halfway up the cylinder which I blanked then 2 at the bottom, the cylinder is taking a long time to fill which is why I’m wondering if it can be done wrong
Is this existing or recently installed?
Is there a gate valve anywhere on the feed from the tank?
Where is the Storage tank,, height relative to cylinder?
Is the vent vertical to storage tank or any horizontal runs?
Same with cold feed to cylinder, what's the run from the storage tank like?
It’s a replacement just installed. The gate valve is opening fully. The storage is in the attic but there is about a 3 metre horizontal run before it drops down to the cylinder. The vent goes straight up through the roof