On 2020-10-18 21:14:05 +0000, Graeme said:

In message , Roger Mills
writes

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 easiest thing to do is just buy a new motorised head. You can get
them cheapest on ebay. I bought a Honeywell with the valve body for
about £30 as i thought it would be useful and indeed have replaced that
too now. Be careful wiring in the new head as if the board is anything
like ours it's rather small and easy to forget what goes where and to
accidentally set another wire loose.