Firstly clean the infra red light cover on the remote. Then clean the receiver end. Your instruction manual should show its location.
Lastly, many remotes have carbon contacts under the buttons. Open remote carefully. Then before taking out any parts take a digital photograph,so you know how to put it back together. Normally the rubber pad and circuit board contacts have excess carbon build up. Clean carefully. I use cotton buds.
Pondlife, November 2008