I have hot water in the downstairs bathroom where the combi boiler is. Upstairs I dont get water unless a) I switch on the upstairs shower then go downstairs and switch on the downstairs tap until the boiler switches on the hot water. Then I turn off the downstairs tap and check that the hot water light has not gone off. B) you can also do it by running the tap on sink and bath and then tweaking them to not full, waiting for hot water to come which could take a minute or 2 then switching to shower then turning off tap. But basically the boiler does not call the hot water easially from upstairs. The radiators are fine in all rooms.

Any ideas