Roger Mills wrote:


I'm not too sure about showing the internals of the mid-position valve
unless you're going to show *all* the gory details - Honeywell just show the
wires disappearing into the case.

Yes, I agree, which is why I've sort of left the internal schematic
vague, but give some idea as to what's going on. I have taken the info
from this document:-

http://content.honeywell.com/UK/homes/FAQ/v4073aop.pdf