On Fri, 29 Jun 2007 13:07:54 GMT, Tony Bryer
wrote:

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.

Got it, thanks. Really apprecieated.

Mike.