I have a pottrton combi 80 boiler. The hot water is fine. The central heating will fire up but after a couple of minutes will turn itself off so I have no heat. A red light on the circuit board seems to be permanently on; also this problem coincided with a drop of water pressure to the bathroom basin which is now has just a trickle from both taps.
I had practically the same problem a few years ago and had to replace the circuit board. I'm having the same problem again after only 2-3 years but can't believe I have to change the board again (£120 or so). I can't see any visibile leaks in the system but the pressure drops over a period of 1-2 weeks.