one of my alarm sensors is constantly flashing?

I have a Eurosec PR5208 rev 1.0. I can't set the system without deleting that zone each time. the sensor is constantly flashing as though spotting an intruder. it is very frustrating. Could I reset the system? Do I need a new sensor for that zone?
If there is any advise or support that you could offer it would be greatly appreciated please. Many thanks