Thanks for the info on reed switches. I know from experience at BT, when
many, many moons ago they used millions of reeds in some of their analogue
Exchanges. Even in static warm and dry environments they eventually would
stick closed. A gentle tap, or any slight vibration would free them, and
they might stay free for many months after, but eventually they would stick
more and more often - just like my wind vane !
A solid state solution, eg. an optical switch, is far better, imo, with the
added advantage of fast switching and no contact bounce issues. I have
mounted my vane close to a wall on a flexible post, so that when the wind
gets up, it knocks up against the wall and hopefully frees the reed switch.
A cheap, but probably temporary solution !