In an earlier contribution to this discussion,
wrote:


Two questions
1. Why does it need the permanent live through the grey wire?
Can I join the grey to the Brown?
(I can send four wires to the otherside of the house that way)

2. Do I need to get this 'certified' because of part 'P' ?


I don't know about any peculiarities of your particular system, but standard
S-Plan works like this:

Each zone valve has two independent circuits - one to drive the motor to
open the valve, and one (volt-free contacts) to switch other things on once
the valve has opened. The motor circuit is driven by the programmer and room
or cylinder stat. The volt-free contacts of all valves are connected in
parallel - with a permanent live as the input and with the output connected
to the boiler and pump. That way the boiler and pump run whenever or or more
zones are calling for heat - but only the zone(s) whose valves are open get
any heat.

If you cross-connect the motor circuit to the volt-free contacts then *all*
valves will open in unison regardless of whether there's a demand in their
particular zone. This is *not* what you want!

AIUI, changes to CH control wiring *are* covered by Part P. But who's to
know when you did it or, indeed, whether it was originally installed as
S-Plan?
--
Cheers,
Roger
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