Start with the obvious.
1 Is the lockshield valve open. Make a note of its position before moving it.
2 Take head off TRV and check central pin moves up and down. This does not involve disconneting TRV body from rad.
Otherwise you have an airlock in the pipes to the 2 rads. Turn off all other rads except one working rad and one of the non working rads. The CH pump should force out the airlock. Once the first non rad is working, open the second non working rad and close the first non working rad.
I have assumed that the two non working rads are not heating up at all as oppose to having a cold area either top or bottom.
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