Then s'evening when me and Roy were out shopping I found my FES control box in the shopping basket. I had obviously knocked it off. I put it back together but it stayed black, not working. I limped around the shop and had a proper look on the way home. Nothing. A couple of beeps when you pressed one button but no other signs of life. Roy said "Battery dead?" but I said "No" as I had changed the battery only last week, but still no life, no combination or order of button pressing brought it back to life.
So in desperation I took the battery out and replaced it in the same position. Lights and display were on again. It works again