Lounge radiator not heating up fully

Hi . We have a 3 storey house and we have recently changed the Trv valve on the lounge radiator to a bidirectional one. Ever since then that radiator is only intermittently getting fully hot. It should normally get fully hot so you can’t hold your hand on it but sometimes it’s only lukewarm and this means that the heating is permanently on as the thermostat is in that room . The radiators in the rest of the house get fully hot at all times so it’s only the lounge one that doesn’t following the valve change . I’ve tried balancing them by closing and opening the lockshield valves one by one but no joy. I’ve even fully closed all the radiators in the whole house apart from the lounge one but still no good. Our boiler is two months old so I don’t think it’s that and the pressure on it is set to 1.4 bar. Can you help ? What do you think the issue is ? Many thanks.