How can I fix my timer on Hotpoint Aquarius Tumble Drier (Model TL61)?

I have a problem with the timer on my tumble drier as it is not rotating and switching off after selecting time duration? The drying process is working fine but only able to turn off through either manually turning dial or switching off at the mains. CI have checked in and around the timer itself and cleared away all dedris/dust ect and all conections seem fine! Can you help please with a solution to this problem?