We have a Ravenheat littlestar, which is around 4-5yrs old. It is serviced every year. Just recently, it has developed an issue with the HW. When the HW is turned on, we hear a click, the fan starts up, then the gas lights. After a few seconds, and this is random, the has supply appears to Cut out, the noises made or just as if the tap has been turned off. After a few more seconds, the fan starts up again, and gas lights up, but on occasion the fan starts up, and then cuts out almost immediately. This can go on at random intervals, and can keep on or after a few times, stops doing this. A heating engineer has been out, and sods law, it would not do it for him. After coming out a few times, at no charge, as he could find no fault, he replaced one of the sensors, I think it was the flame sensor, but no luck. I did turn down the HW dial on the boiler, and this seemed to do the trick for a day or so, but nw the same again... Does anyone have any ideas as to what this may be. The CH is absolutely fine, and does not cut out.