How to remove old radiator valve head

[FionaM]

Hi,

One of my radiators is not working, completely cold while the others are blazing. I have read that this could be caused by the pin inside the valve being stuck. Unfortunately I cannot remove the old Giacomini head - does anyone know if there is a knack to doing so for this particular model? Pic attached

Thanks

 

[TCCHeating]

Pull the bottom locking ring up. Then you should be able to remove the head