Quite common as heat rises, you can trap the central heating flow to stop this. As heat rises, if you drop the flow down before going up, the heat cannot rise naturally.
if it is fully pumped system it would most like be the heating zone valve passing or the 3-port valve passing.
It could also be reverse circulation, but it is unlikely, as if it were it would have been present since the day it was installed
easy cure? yeah, turn all the radiators off! :P
Your local engineer should have no trouble correcting the fault, unfortunately i can't give any other advice without any details of your system.