Ford KA Heater direction control doesnt work?

Hi, my ford KA heating direction control dial has stoped working. It is the one which selects to have demister on or the blower going up or down etc. It is not electronical i think when it turns its supposed to move the way the blower directs manualy. however this has now stopped working. has anyone got any ideas to what has caused it or how to fix it?

Lee
February 2011