Bosch WFB2005 Cycle Starts but programme dial doesn't turn

Hi could you please help we have a Bosch WFB2005 model washing machine and have just started to experience a problem. We load the machine and set the programme dial, the washer fills up and appears to be washing as normal but when you return to the washer the dial still shows as being at the start of the cycle selected. It is no longer moving automatically meaning the wash is not progressing and doesn't end unless we move manually the dial through the cycles. Any ideas what may be causing this.