Sorted. If it help others the interior rear wall of the freezer compartment can be removed to get at the fan. TURN OFF AT MAINS. Empty freezer. Remove shelves. On the rear wall are a number of circles in white plastic, remove these - they are screw covers - using a cross headed screwdriver remove the 7 screws (the bottom two do not have covers). Now lift the rear panel from the bottom upwards and outwards carefully. Once you have removed the lower panel the top one can be removed - carefull you don't pull out the temperature sensor wires. The fan can now be seen but look at the rear of the remove upper back panel and you may see lumps of ice attached to the white insulation. Remove these ice lumps and some of the insulation where the ice is trapped. Replacement is the reverse of removal but don't trap the temperature sensor cable and don't forget to put the screws and covers back. Tuen on the mains when finish.
Geoff Parselle., October 2007
