"Set Square" wrote in message ...
In an earlier contribution to this discussion,
Ed wrote:


The spring return is smooth and fast, no problems there. As I write
the system is behaving fine so it's a little hard to do diagnosis.
When I did the wiring checks I did find one wire in the connection
unit that could have been tighter but really didn't seem loose enough
to be a troublemaker. I've given it a little tweak anyway so now I
just have to wait for the next cold morning. Still baffelled by the
way it sits on AB with ALL wires disconnected, what is holding it
there? If you pull the power at the FCU it spring returns sharply...
Watch this space...


It is possible for mid-position valve actuators to get "confused"
sometimes - maybe a microswitch doesn't quite make when it's supposed to, or
something like that. Sometimes when this happens, the thing can be reset by
removing all the power and starting again. This may have happened in your
case.

If you disconnect ALL 5 wires to the actuator, this should have the same
effect as pulling the power. Can't explain it if it didn't! Are you sure
that *something* wasn't still connected?


Sure as can be, Synchron has only two wires, both disconnected, +
orange white and grey for good measure, stays put on AB until you shut
off at the FCU, then instant smooth spring return. Anyone for an
exorcism?