This boiler has a preheat for hot water and will fire up occasionally to heat the hot water in the boiler to around 60 degrees, it is possibly just firing up for the preheat but the diverter valve is passing and allowing the radiators to heat up. the selector switch in the middle could also be broken and stuck in the heating position, turn the switch to the off position and the display should go blank, if not then this switch is most likely the problem, hope this helps.
J
December 2008