Just wanted to thank all contributors to this thread - I mamaged to fix the problem foillowing advice from philvbarnes and cookiels21 and now have the fan working on all settings and brownie points from the wife.

I'd be grateful for some advice on solving the cause (water leaking in past pollen filter). I removed the back cover and can the concertinered paper, and in doing so broke what was left of the seal between the windscreen and the cover. It looks like a thin piece of foam double sided sticky tape that I need to replace - can anyone recomend a source for this? I can see some wider 'HEAVY DUTY DOUBLE SIDED MOUNTING TAPE 5m x 24mm' tape on Ebay but am not sure that this is designed for outdoor use.
Thanks in advance, G