maybe the outer ring on the timer knob has come off and been put back on wrong giving you wrong setting when you choose a setting. if it does come off easily, take it off and on the inside of the ring you will find a tiny groove. now, on the timer knob, run your finger round the rim to locate a tiny bump. this should fit into the groove when it is put on giving you an accurate setting. i suggest gluing it on to avoid it happening again.