Do you have a room stat somewhere and are the radiators in that room fitted with TRVs because you may have a situation where the stat is calling for heat but the TRVs are set below that temperature and are shutting off the flow to the radiators. You should also have at least one radiator with no TRVs usually the choice one is the bathroom radiator this acts as a bypass in a situation where every TRV has shut down.

If you have the above situation a temporary solution is to turn the TRVs in the room with the stat to full on and let the stat control the temperature..

Richard