Indirect hot water cylinder pipework

[Stewy801]

I'm a bit confused with the plumbing to the flow on the coil (28mm). At the elbow it is T'd in 15mm to the attic. I can't trace the pipe as they are under a floored attic. Is it going to the header tank and if so why?

 

[Puddle]

I'm a bit confused with the plumbing to the flow on the coil (28mm). At the elbow it is T'd in 15mm to the attic. I can't trace the pipe as they are under a floored attic. Is it going to the header tank and if so why?

Well if 15mm it should go to the header tank and be the cold feed that fills system up with water,you should also have a 22mm open vent and expansion pipe that sits over the header tank,however there are variations and short cuts people make.