In an earlier contribution to this discussion,
Andrew Gabriel wrote:


There's no hunting in the mid position unless something's broken
or wasn't wired properly. The motor's rotor is locked in mid
position by feeding it DC (or half-wave rectified AC), which is
generated in the head by a diode in the circuit.


I have to admit that none of mine (and I've needed several in the last 18
years) have actually suffered from hunting, but several people have
mentioned hunting in recent threads - so it *does* appear to be a problem.

But the fact remains that the thing is overly complicated and seems prone to
more frequent failure than its 2-port cousin. One day when I've got nothing
better to do (so it may never happen!) I'll count up the number of CH
problem threads in uk.d-i-y where the ultimate diagnosis has pointed to a
problem with a 3-port valve. I shall need a lots of hands and feet to count
them!
--
Cheers,
Roger
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