In an earlier contribution to this discussion,
The Natural Philosopher wrote:

Roger Mills wrote:
If the valve is too stiff for the spring
to move, it will remain open - with the symptoms which you have
experienced.

That was my problem..gearbox went strange and the spring couldn't
close it. New motor and box fixed it.

That's another possibility. What I was actually referring to was the
mechanical (wet) part of the valve being too stiff for the spring in the
actuator to move it.
--
Cheers,
Roger
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