Cold Radiators

Merry xmas everyone.
I've a studio flat in my house which has 4 radiators and out of those 4 one is completely cold and the other is partially cold. I've 16 radiators in the house which are powered by a Vailant system boiler. To fix the problem, I spent some time today to balance them, primarily the upstairs one by completely closing the return return valve on all the rads and then opening them up about a quarter. This has improved the situation somewhat in the studio by getting the one a bit more hot but its still cold in the middle from the bottom. The other one is still cold, though I can feel the pipe with thermostatic valve getting some hot water.
I've the feeling the hot water is not getting distributed enough to those rads, any idea what can I do to improve the situation?

Check TRV's on rads (that have them),to establish if the pin below the actuator head is moving freely up and down ,and their lockshields are fully open ,on rads that do not heat up.
On one radiator that doesn't heat up ,open its TRV fully . On every other radiator close their TRV ( or wheel head if no TRV)
Run central heating and see if the rad that has its TRV open ,now heats up.
Advise the result.

have you bleed all the radiators?
Also if a pressurised system, check the pressure before hand , as bleeding will decrease the pressure probably to zero, so you may need to re-pressurise and then carry on bleeding

Pump size maybe

I had checked the TRV on the one that's not heating up at all and the pin is moving freely. If I press it, it goes down and then gets back to its normal position. Lockshield is also fully open.
I've bled the rads, water is coming out from the problem ones and boilder pressure is 1.5 bar.
I like the idea of closing the TRV on other rads to divert all the hot water to the ones NOT working.
I'll do this later today and would update.

Closed all the TRVs as terryplumb had suggested apart from the ones I'm trying to fix. The one which was partially getting hot seems to be getting a lot more water now. Its proper hot but still with a small bottom middle part which is cold.
The other one which wasn't getting warm at all is also warm at the top but nowhere near it should be. But I'm not too concerned with this one because as long as one of these two rads work its good enough.
What does this prove? Is my boiler not powerful enough to provide enough water to all of these rads or the problem lies elsewhere?

If you now turn on all other rads TRV's ,does the one that now heats well continue to do so ?
If so, it's a balancing issue most probably.