Hi, thanks for the really quick response Doddy, appreciate your help.

I've attached photos showing the relevant part of the controller board.

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"Green to +, black to -" - yes, this is how I had it previously (and red to S). So it perhaps seems like a simple case of having put the plug on upside down onto the controller board?

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This is the actual switch I have (though just to add to the confusion, it's shown there with yellow in place of green, black and red are shown correctly).