On 04/10/2020 11:45, F wrote:
When the room stat is calling for heat I assume the valve is driven open
and held open but is it driven closed once the stat is satisfied or the
hold released and springs are left to close it?

springs close it. suppsodely 'failsafe' on power loss


Though the fault has rectified itself a couple or three times, am I
right to assume I'm looking for a new actuator head?

No. Often the problem is scale/corrosion inside the valve body.
take the head off and wiggle the valve shaft. If it doesn't move freely
you need a whole new valve, and unless you use freeze spray or have
isolation valves a drain down of the whole CH or HW primary circuit.


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