In an earlier contribution to this discussion,
Costick wrote:

Hi, I have been perplexed by advice from suppliers' literature. If I
am going to install my own CHS, I need to know how to design it to
avoid beginners' problems - like where to attach the feed and
expansion and drain pipes.
The advice I have seen in diagrams is for the feed and expansion
pipes to be separately connected to points just after? the pump - a
specific distance apart. The pump has to be low in the system for
some reason, and just after the boiler. This means two extra routes
from the top of the house to the bottom, just for these minimum-flow
pipes.
Has anyone any experience of feeding the system near a top-floor
radiator? Why is an expansion pipe necessary if the feed is only ever
closed for draining?
Is there anything wrong with putting the pump near the top?
Sorry if these questions are basic, but I can't work it out. Perhaps
I should not attempt anything so challenging without expert help.

Many of these issues only exist in open vented systems. If starting from
scratch, I would be using an unvented (pressurised) system. OK, these have
issues of their own - but they do eliminate a lot of the problems of vented
systems.
--
Cheers,
Set Square
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