On Sun, 18 Oct 2020 22:14:05 +0100, Graeme wrote:

If the shaft moves freely and the actuator doesn't whir closed,
the
problem is with the actuator. Otherwise, it's with the valve. In
most
cases, you can free a stuck valve by working it backwards and
forwards
with a pair of pliers.

Thanks Roger. Almost certainly the actuator, as the shaft moves freely
and has not closed in that water is still circulating beyond the valve
(and heating radiators) even with the actuator completely removed.

The valve needs the spring in the actuator to close. If you manually
close the valve does the flow stop? Perhaps the ball has
disintegrated. Does the actuator motor open and spring return when
not on the valve?

--
Cheers
Dave.