I have just had a ravenheat boiler CSI 85B(T) installed. The problem is that the boiler will fire up okay and then after a few minutes the overheat/flame failure light comes on and then nothing works. It does this on both the hot water only selection and the ch and hw selection. I have to switch the boiler off and restart it but the same thing keeps happening. This is a brand new boiler and I had the same problem with my old one, so the problem is obviously not the boilers but the system. All the rads have been bled correctly and all valves are open. I'm rapidly losing my sanity as I have had no hot water for a week now. Can someone please help me!!