poor hot water from a combi (halstead ace high 102)?

Hello Mark,
Sounds like the heat exchanger to me, even when you flush the system you can still get debris etc caught in it, before spending any money take the heat exchanger out, do this by draining the system, including the radiators as the same water is used for heating and hot water for indirect heating, and isolating the water supply going into it, remove the heat exchanger(normally a couple of screws and get ready to catch some water left in the system) and flush it out with water, if debris is the problem this is when you will see it, usually a black flakey material, put it back together and refil the system.
Hope this helps,

Paul
March 2008