On Fri, 29 Jun 2007 10:56:20 +0100 Mike Barnard wrote :
1. Can I use a common return? (There was an answer in the
previous thread but it made no sense to me.) If zone 1 is
operating and zone 2 isn't, can there be a problem with using
common returns?

To stop the possibility of reverse circulation you need to bring all
the zone 1 returns together before linking to the common return, do.
zone 2. If (say) the return from zone 2 passes across two different
returns from zone 1 there will be a pressure difference between these
points and a portion of the flow will go up one return, through the
rads, along the flow (in the reverse direction) to the second rad and
back along its return.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk