Broken plastic bolt inside thermostatic radiator valve

[Best]

Get it replaced as soon as you can.
You have clearly broke part of the gland leaving the final gland O ring seal on the pin exposed.

 

[Best]

Did it have something like this on top, which you have broken?
https://www.googleadservices.com/pa...ahUKEwjhg4LGyKTTAhXMCcAKHfwZALsQwg8IHg&adurl=

No Stani, - I am fairly sure what the OP meant is they broke the gland nut, which is plastic on that particular TRV.
You can see the wee O ring exposed

 

[stani]

Yea can see it now, on iPhone it's not good, iPad is better picture. Thought the way it was described it was the dust cap.

How do you say thanks with these little whatever they are things

 

[Best]

Yea can see it now, on iPhone it's not good, iPad is better picture. Thought the way it was described it was the dust cap.

How do you say thanks with these little whatever they are things

If you click on each wee symbol to see what it does and then you can undo it (undo to the right).
The thumbs up is a Like