Thank you for the help. I bled both sides locked off and they were fine. So next I opened TRV fully and only just opened the lock valve. This showed promise with heat actually rising a little. I opened the valve a little more and the radiator is now after a little while at a good heat. I believe this comes under balancing the radiator which I read in a DIY book in the 90's. So try shutting valve nearly off and see what happens. As mentioned before the hot water was just running straight through the easiest route. Thanks to all and good luck.
I've had 2 of these in different houses and neither got hit. I just think they're not great, badly made and hold so much water that this must be part of the issue.. I replaced the rad with one not so high which is alumnium and it works perfectly. I have 2 other column rads that are shorter but longer and these operate fine.
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