Central locking

Hi, thanks for the reply, I cannot hear any hum from the rear but when you lock it with the key you do hear a short quiet beep ( sounds like car horn but a lot quieter) As far as I know everything else is working from the key all the doors open, petrol cap and boot opens,. I will have a look at the pump when the weather gets better. Is there any way of testing it and if I was to replace it, would the keys need to be re-programmed?