How do i turn the automatic timer off. My oven has stopped working since my mum played with the timer, it just shows an A lit up in the top left corner, it has done this before and the blanks screen just started flashing a time and from then i could work it again....but every few days it stops working again and just shows an 'A'. My oven has 6 buttons, from left ...a bell, then crossed out heat symbol, then heat, then a minus, then a plus , then a hand symbol.