In an earlier contribution to this discussion,
Andy Johnson wrote:

Set Square,

Thanks for replying - you've made a lot of things clearer. And you're
right. I have two two-way valves.

I'm not clear what the 'volt-free' contacts are. Is this the
microswitch in the motor housing that John mentioned, or is it part of
the valve itself? I removed the motor cover, and unscrewed and
lifted-out the motor, and I could see a green plastic microswitch
underneath with a kind of cam that nudges it as the valve turns. Is
this what you mean?

Andy

Yes - it's electrically separate from the motor supply - and can be used to
switch anything that needs to be switched when the valve is fully open. In
an S-Plan configuration, it is used (in parallel with the contacts on the
other zone valve) to switch the boiler and pump on. When the valve is open,
the cam should operate the switch in a way which closes its contacts.
--
Cheers,
Set Square
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