I suspect an airlock. I said how to cure an airlock in the last post... basically flush it out by attaching hosepipe to hole where bleed valve lives. Had exact same problem as you and this fixed it.
The problem looks to be way before the rad,
Not necessarily. Basically warmth is spreading down the pipe towards the rad by convection. It sounds like you have no flow through the rad so it CAN be the rad that is preventing this - hence me asking about the valves.
Sounds to me like something is blocked.
Blocked can be
valve not open
TRV pin stuck
PTFE tape wrapped over end of pipe when wrapping round an olive (have seen this)
airlock
Does water come out the bleed valve when you bleed. If YES then you have got water pressure to the rad. However it can be water from flow or return and one or other can still be blocked. So now you need to determine if both valves are allowing water to pass.
Make sure heating is off.
Turn OFF the TRV but open the lockshield valve (the other one)
Bleed the rad for a couple of minutes.
Does water keep on flowing?
If YES then the lockshield is allowing water to pass. If NO then it is blocked.
Turn OFF the lockshield valve but open the TRV
Bleed the rad for a couple of minutes.
Does water keep on flowing?
If YES then the TRV is allowing water to pass. If NO then it is blocked.
Report back.