Radiator won't turn off

[SolaceMan]

Radiator is still getting hot even when the thermostat is set to zero. Turning the other valve does nothing. Both valves (the thermostat and the other one) are now turned as far clockwise as they will go and the radiator is still getting hot. Photos are below. Any help would be much appreciated.

 

[Aquarius]

Trv (thermostatic valve) pin not engaging would be my assumption. The other one, did you remove the cap?

 

[SolaceMan]

I didn't think you were supposed to remove the cap for that type of valve. When I've tried it before, I saw a tube with spines on the side that are gripped by the cap (picture below) and someone on this forum said that it should be turned with the cap on.

WIth regards to the trv, it must be doing something, since the radiator gets quite a bit louder when I turn it up - it's just that doesn't seem to properly shut off. If there's a problem with the pin, how would I fix it? I saw some tutorials online for removing trv heads but I was hesitant to try it here since this one looks a bit different (there is a hexagon rather than a ring underneath it).