Hotpoint Dryer VTD00 Big Timer Problem!!?

My timer spins round too quickly when it is turned on, causing the dryer to stop after 10 mins (instead of 2 hours!!). So I have to keep resetting it back to the beginning. Any ideas what it could be - is the timer gone?? Is it worth replacing? The dryer is 4 years old and it's had this problem for about 6 months. Don't want to really have to keep standing next to the thing to wind the timer back every 10 minutes!