In an earlier contribution to this discussion,
asalcedo wrote:


Concerning the 230V differential, if the terminals of the grey cables
were fully isolated it should not be at or near earth potential and
then it should not read 230V but 0. If the grey cables were connected
to neutral, then connecting them to live would create a short. So, I
still think that my precaution was appropriate, am I wrong?

If the grey cables were connected to neutral then you would indeed get a
short if you also connected them to live! However, I presumed that you could
see that they were not *directly* connected to anything. If you were
measuring between live and the grey wires while there was a demand in at
least one zone, one or more valves would be open and its/their microswitches
would be closed - thus connecting grey to orange. Since orange is connected
to the boiler, it would be held at earth potential via the relatively high
impedance of the boiler control circuits. What you actually measured would
depend, to some extent, on the impedance of the voltmeter being used. What I
was respectfully suggesting is that you really need to have a thorough
understanding of what is going on, and an ability to interpret what your
meter is telling you, before having the confidence to make further
connections.
--
Cheers,
Roger
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