if the pressure goes to zero and you have to refil it, it won't be a fractured plate heat exchanger as this would cause it be constantly on 3bar. your expansion vessel has failed (big red cylinder shaped thing at front of boiler) this will need recharging to 1bar using a foot pump (be sure to do this with the safety valve open) it may have failed completely and require replacing. try recharging first though as it will be cheaper. hope this helps!
andy gas man, March 2009
