My bathroom radiator is plumbed into the hot water circuit (2 x 2 port system), which I think is not unusual but I would have thought it should be connected before the 2 port valve so it is always on when hot water is on. As it is in fact fed from after the valve, when the hot tank is up to temperature and the valve closes, the bathroom radiator goes cold. Is that normal? It means the better insulated your hot tank is, the colder your bathroom is!