On Mon, 10 Aug 2009 04:01:11 -0700 (PDT), Lee Nowell wrote:

Also, any advice on whether a wiring centre is a good idea as they seem
to be very expensive given what they appear to be....

A normal wiring center won't cope with that number of zones.

For the system here (just four zones 2 x HW, 2 x CH, with shared
circulators for the two HW zones and two CH zones). I bought a small
(three row) DIN rail enclosure and lots of terminals. All the wires
from the valves, thermostats, timers, etc come back to that box so
and config changes are just jumper changes in the box not house
rewire jobs.

The logic for the pump, boiler and pump over run control is done with
half a dozen DIN rail mount minature relays. If I was doing it again
I'd find a large enough PLC, even easier to adjust the logic. I'd
retain the normal programmers as they have nice simple buttons and
displays that ordinary people can understand.

--
Cheers
Dave.