What could be causing my timer control to stick ?

I have a Sangamo 410 combi water/heating timer control which has recently stopped turning/advancing the clock timer (physical electromechanical timer).
The actual Heating & Water can be switched to be on constantly and works OK, but if you try to schedule it by the timer, it won't come on, as the timer control is stuck and never advances.

I can hear the device "clicking", which would suggest that power is getting to the device, but think that maybe something is wrong with the motor which turns the timer !

Can you help ?