My Vokera Maxin 24e is not working?? ?

My boiler was serviced around 7months ago, after a small dripping of water from the bottom of the boiler, by a qualified plumber. Since then I have had nothing but bother with the thing. At the moment when I turn the central heating on the red light on the front of the boiler comes on after around 2 minutes, once this is pressed the boiler comes back on but only for around 30 seconds. The water will now heat up but for only around 1 minute and thereafter returns to freezing cold. In addition, I have just checked the pilot light which will not fire up when I turn the CH on or run the hot water???