It may need to be reprogrammed to the transmitter. When you but the receiver, every one is identical, but there are about 2 million different code variations for the transmitter (the keyfob)
Peter will have programmed your receiver to recognize your transmitter, but sometimes something happens that wipes the receiver's memory. (Extremes of hot or cold, EMF radiation etc)
To reprogram them is a simple, 2 minute job. Details of how to do it are on his website.
-Philip
(Also, if the receiver gets wet, it will stop working instantly [voice of experience] open the case and dry it with a hairdryer on the "cool" setting, then it should be fine)