"TheScullster" wrote in message
...

"Anita Palley" wrote


On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?

Yes

15mm pipe from the stoptap to the boiler with associated elbows etc
creates a pressur drop.
Using 22mm right up to the 15mm boiler connection guarantees minimal
losses before the boiler.

Yep! You could have 25 litres/min and 3.5 bar at the stoptap and with
lengthy 15mm pipe with elbows have 20 litres/min at the end and much reduced
pressure at the end of the pipe.