My potterton ep 2000 controller is it worn out?

When both switches (ch and hw) are in the on or 24hr position on the controller the motorised valve should go to the mid position it doesent it just goes over to the ch or hw on the valve.The only time it goes to the mid position is when both switches are off.The motorised valve has been changed.Do i need a new controller it is 21 year old ?