Help - my boiler will run on CH for about half an hour before stopping & the red fault indicator light flashes fast. I reset & leave a while before switching on again with the same result. The HW usually works but not when the CH is on, again the boiler switches off & the red light flashes fast. I've scrolled through the other forums & I'm led to believe it could be an overheating problem or I need a new PCB? Any thoughts?