how to fix?

The battery is located in the bottom of the main box it will have a red and black lead comming from it, you will also have to disconect the mains by either removing the fuse from the spur (if fitted) or the small fuse from the holder where the mains is connected bottom right i think, once this is done the outside bell may ring if the battery in it is working but it should time out after 20 mins

simon
June 2009