pressure gauge kept showing a reduction in pressure so i replaced the pressure relief valve still same problem so replaced diverter valve diaphram not sure if this has solved this problem yet .Other problem the DHW is not functioning properly the water doesn,t come though very hot .Burner lights up as it should when demand for CH and DHW good blue flame .CH works well nice and hot .When hot water tap is turned on burner ignites but water is luke warm the CH system also starts when turning on hot water tap .DHW does come a little warmer when rads are up to heat .When feeling the pipes that leave the water heat exchanger the pipes to central heating are hot but to the DHW is luke warm have I just answered the question is the water heat exchanger US appreciate any help thanks