Double Radiator not hot

Old radiator wouldn't get hot, so I replaced it with a new one and new valve's, And now it get quite warm at the back of it(double panel) but the front one is barely warm. I tried bleeding it, but no air comes out, tried balancing the radiators, but that does nothing, rest of the radiators are hot. Pipe and valve going into the radiator are very hot. Unless there's air in the front panel of the radiator that won't bleed out. Can anyone advise me what I'm doing wrong please.

Some older radiators had separate bleed points for front and back panels.
Picture of radiator and bleed point(s) might help.
How did you balance the system?

1. Your radiator has a single bleed point so its not that. Presumably you are getting water out of it when you bleed it.
2. Try turning off all the other radiators and see if the offending one then gets hot. Don't touch the lockshield valves on the others or you'll end up rebalancing. Just shut off the TRV / wheelhead valve for each. If it does get hot its likely to be a balancing issue.
3. Try taking the thermostatic head of the TRV on the offending radiator. If it then gets hot its possibly a faulty valve or even a faulty radiator.

Incidentally, wrapping the threads of compression fittings with PTFE tape does no good, and in some cases can damage the nuts. The seal is made between the inside of the fitting, the olive and the pipe. The angled edges of fitting and nut come together and crush the olive onto the pipe.

Yeah I do go over the top with ptfe tape, it's just weird that the back panel of the radiator get quite hot but the front of it is just warm.

If the back panel is genuinely getting properly hot all over and the front panel isn't, I'm left thinking internal blockage in radiator.

Doing my head in. The old radiator was never hot. I thought buying a new one and valves would solve it, Some how makes me think it's something to do with the pipe work or crap in the pipe just before the radiator. Do I need the drain the radiator out and fill it up again.