Hi guys, have come back from friends house and convinced him to take tape off re-set button on his Halstead Quattro Gold. While i was there, i took case off boiler just to see what was going on. When hot water is turned on the DHW exchanger heats up really hot but, the hot water out pipe is only mildly warm. The return pipe on the CH side on top of the DHW exchanger gets scoldingly hot right back as far as the pump. If you turn the water tap down to restrict the pressure called for, the hot water out pipe from the DHW exchanger gets really hot then the boiler cuts out and when the pipe cools down it comes back on. I have watched the switch pin on top of the diverter valve and it reacts really quickly when you turn hot water on or off. He still has problems with CH pressure drops to zero the day after he has had it on. I put my finger under PRV pipe outside and its wet/leaking. I checked expansion vessel valve to see if water or air would come out and air came out. He has someone coming in tomorrow but doesn't want to be ripped off as he had the diaphragm changed in the diverter 10 months ago and paid well over the odds. Can you let me know what you think the problem might be so that he is armed with a bit of knowledge for when the guy comes. Cheers.