The switch that operates the fan on/off (speed 1) has probably failed, I have seen this 1st hand. - there seems to be a problem getting the switch itself but replacement assemblies are available from around £30 +p&p - UK Whitegoods have best price so far. Some soldering is needed though as original wiring is used to connect to new assembly. So you may need help if you have no soldering equipment.
Dave, February 2010