I have a ravenheat csi85 boiler, the hot water works fine. The central heating started switching on /off, it was sufficient to heat the radiators but I didn't know how long it would last. I discovered that if Iturned on the hot water tap it seemed to kick start the CH and it would work again for a few days. It got to a stage when the quick fix didn't work! I found out with help through this site and nowhere else that the problem is almost certainly the fan modulation pcb board. 5min to fix and working perfectly. HW works at a higher voltage so when the CH starts up and stops, it is this board that is failing! I hope this helps others out there!

Gordon, April 2012