My boiler is working fine for the CH side of things. When I run hot water the overtemperture trip goes after a few minutes. The hot water also seems to go cold then hot when it is running. I have checked the overheat thermostat and thats o/k. Thermistors also seem to be o/k with correct resistance values vs temperature. I have also reduced water pressure with valve on diverter but still seems to be a problem. Appreciate any help!!

Gary, May 2009

could be plate heat exchanger

b, May 2009