Thanks for all the comments and apologies for the delayed replies.

Dealer diagnosed multiple motors problem, booked it in for 1.5 days to do the job then phoned back to say that VW forbid them to do the work. I still need to chase them for a written statement of this in case it ever goes totally fubar.

As for the symptoms, apparently it is "okay for there to be some clicking that goes away once the heating system has warmed up". Woopie doo. Mine clicks whenever it feels like it, hot or cold.

If anyone can give me the number and other details of the recall on the control unit I'd be very grateful.