rest or mid position anyway, I see the normal S-plan wiring will do

Meant Y-plan. (It was late, I was tired....)

Re-reading my question again. Honeywell and the FAQ don't seem to concur on
the wiring, although I recognise that the definition of ports A & B are
transposed between them.

Still a bit concerned about leaving the valve with 240v on grey(hold last
position) for extended periods, and 100v output on orange is neither 'on' or
'off'.

Toby.