We have a 5 year old house hence a 5 year old heating system, it is a sealed system and all radiators have TRV except for hall radiator where the wall thermostat is. The problem is that some of the radiators remain cold while the others are hot, I have checked the TRVs and all of the pins work fine. There appears no logic to which radiators are cold, for example on the top floor the radiator at the front of bedroom 1 is cold, the radiator at the back of the same room is hot, in bedroom 2 on same floor both the front and back radiators are hot. On first floor both radiators at front are cold the ones at back are hot. In living room the front radiator is cold the rear is hot. To add to my confusion for most of the cold radiators the outlet pipe is hot the inlet is cold. I have bled the system and there was no air in the radiators. If I turn up the pump to full speed then the cold radiators get hot but the outlet pipes are very hot and the inlet pipes are luke warm. Any ideas what I can do next?