Potterton kingfisher 2ignition problem?

OK. We have a Potterton Kingfisher II boiler. There is an ignition push switch and a black dial (settings: off, spark, flame). We can get the pilot light on when in spark mode, but the dial has to be constantly pushed down. IT SHOULD BE TURNED TO FLAME and the pilot light should stay on for the cycle, but the flame goes out instantly and it can not be ignited in flame mode! So how do you keep the pilot light on and burning in a Potterton Kingfisher II? Is there something we are missing in the sequence? Can anything else be done?