my schott ceran hob is flashing 4 red L,s how can i fix it?

I had the same problem. I do not have a manual and so I assume 'L' means lock. I played about with the controls and discovered that by pressing '-' and '+' together immediately after I switch on the hob it works, but only with one set of '_' and '+' . If I do not press these buttoms immediately after switch on it does not work I have switch of and on again.

dave
August 2010