@tom thanks for your detailed response. i actually tried looking for the ‘blower fan controller’ as per http://www.autoinsider.co.uk/problems/problem-10641-citroen-xsara-blower-speed-control-module.php earlier today but couldn’t find it and no reference to one in haynes electrical section..
so ignition hack may not work?
edit: above link not my car so maybe picasso hasn’t got one or do you mean the rotary speed control on the dash?
ps, hope the mouse that took up residence in my car at about the same time had nothing to do with it;)