I'm about to wire up an extra CH zone, the thermostat will call the
valve, and the valve's auxiliary switch will call the heating system.

However I find that the system is wired using an Honeywell 42005748-001
wiring centre. This appears to have no provision for a second (third
etc) zone.

http://www.uk-plumbing.com/brochure/...Centre4200.pdf

Does anyone know how to wire the zone into such a wiring centre? This
photo shows how it is currently wired:

http://bit.ly/6Iv5Lg

If I just connect it to the roomstat terminals in parallel with the
existing roomstat this will also call the main S plan zone valve.

If this is too complicated, I may just replace the wiring centre with a
10-way junction strip. I'll want to add more zones as I go through the
renovations.

I was planning to place the new zone valve in parallel with the
existing CH zone valve, so either one or both could be open. So the
new one would be tee-ed in at the same point that the DHW feed leaves
the pumped feed from the boiler. Bottom of is photo, near the
broomstick top:

http://bit.ly/54spPu

The zone return just joins the main return wherever convenient.

I hope that's right?

Thanks,
R.