TRV HEAD valve servicing / teardown. Radiator

No heat from radiator? The TRV pin or TRV head could be the issue
this video shows how to service the TRV head , unlike most other videos
Note : if the radiator works/heats with the TRV off the radiator but doesn't with it back on , then its likely this video will help you.
after the fix you should be able to put the TRV head back on the radiator and tighten without pushing down (ensure the TRV head is in the full open position before re attaching)
just like the pin of the valve attached to the radiator can become stuck open so can the pin inside the TRV valve which reacts to the room temperature
note: when re attaching the main body , it does actually matter where you line up with, you need to ensure the valve can still move full open and closed (small tabs that stick out)