It could be that your hot water flow is too high to be picking up enough heat in the heat exchanger. With my 24CDi the hot water flowing from a hot water tap is much less than the flow from a cold water tap. There should be a little white disc in line between the diverter valve and the secondary water heat exchanger. This is called the domestic hot water restrictor (or regulator) and limits the hot water flow to about 8 litres per minute. I would check that this is fitted and if so that it is in good order, there is an 'O' ring between the two halves of the assembly that sometimes perishes.
Richard
May 2008
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