heat switch does not turn off the radiators upstairs?

when I turn the heat switch off, but keep the water swith on, the upstairs radiators are still very hot. The problem is in the winter the upstairs is far warmer than downstairs. In the summer when the heating is not required I have to turn all the radiators off upstairs. I am told by my heating engineer that this is good as I have good gravity. This did not happen on my old boiler.