boiler not firing?

my worcester bosch greenstar 30cdi gas boiler (normal--NOT coombi) has digits 25(sometimes changes, like 20 or 18) and % on display FLASHING alternately. The ON/OFF indicator blue light is continously ON. Itried pressing the RESET button. ALL lights come on for a second and goes off. There is a humming noise is a couple of seconds. So no hot water or heating. Please help. Thanks.