Hello Pamela, the timer drive shaft is around £18. Do you suspect this as the timer knob just goes round and round?
This is a job that really requires some knowledge and is not for the faint of heart!
A video of that job is here: http://www.espares.co.uk/part/tumble-dryers/bosch/p/1088/856/0/0/144598/tumble-dryer-programme-kn.html
OJ
September 2011