I have eight radiators and when heating is on some are hot some are warm some cold.
I have bled all (although no air release in any)

Have you ever known them to get hot? It could be a number of things causing this.
1) the radiators need balancing. Simple fix adjusting the lock shield valve on each rad.
2)the installation pipework could be wrong, major problem, floors up changing pipework.
3)the TRV valve might need freeing up on the head, take off Actuator head and press in the pin with a tool.
4)blockage in the radiator from sludge, system may need to be flushed through.
5) could be an air lock, shut off all rads, open one rad at a time.
6) easiest of all, is it turned off at the radiator, if so turn up the TRV.