jaime wrote:

Hi.

I've spent a few hours recently up in the loft, trying to understand how
my central heating/hot water plumbing works. One point that baffles me
is a copper pipe connecting the flow pipe (from the boiler) back to the
return pipe (to the boiler), situated about a meter before the two pipes
enter/exit the (indirect) copper tank. This "connection" has a
wheel-handled valve half-way along it (I assume, from the wheel-handle,
that it's a gate valve).

In case it helps, here's a poor quality ascii-art picture, with
connection to feed/expansion tank and overflow pipe omitted (it should
work with a fixed-width/monospaced font):


To Rads
^
^
Flow from boiler---+---Pump---Diverter Valve---Into Copper Tank
|
Valve
|
Return to boiler---+-------------------------------From Copper Tank



My questions a what's the purpose of the pipe, should the valve be
open or closed during "normal" operation, and why would I ever want to
change the valve's setting (open/closed)?

Many thanks, Jaime

Don't buy anything from Maplins. My broadband started to go slow and my
ISP said I needed a new filter. Maplins said I needed new cable. I
bought new cable but the broadband speeded up again - must have been
BT. So I took the cable back. But because it had been machine packed
there is no way I would return it "in the same condition". The cable
WAS "in the same condition". But the idiots said the packing had to be
the same -- impossible!

If they want to get things back "correctly" they should use packing it
is possible to pack.

Every other company I've taken anything back to, in living memory has
accepted it back with full refund.

Except Maplins.

Don't even think of shopping with them.