It's almost like your connections are mixed, in that the "hot water" is on the CH side and heating is on the DHW side.
The Combi units have an automatic prioritiy for the Domestic hot water. But this shouldnt really happen unless you have a secondary pump running the central heating.
THere are 4 connections, 2 are 1/2 inch pipes (cold supply and hot out), and 2 3/4inch pipes (domestic supply and return). Make sure those are connected at the right spots. There could be a bad part if the connections are proper, so it should be covered by warranty if that is the case.
G
February 2010
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