Radiator missing a control - help!

[OhThatChicken]

Really hoping attaching the picture works!

My poorly mum is coming to stay for a few days and I'm just getting the spare room ready for her. Went to turn the radiator on as, apparently, our last guests from a couple of weeks ago preferred to sleep without heating on in the room so turned it off.

The whole top of the radiator control has come off in my hand.

Trying to put the control back on just sees it twist round without moving anything if that makes sense.

The radiator is off. I'm assuming the line on the top show how the valve opens and correlate with what would be the controls on the twisty bit. Is there a way I can turn it without the top on, if so which way should I do it and how without crapping up the whole thing?

If it's a major issue I will get someone else but I won't be able to do it before my mum is due so hoping a wise DIY knowledgeable mumsnetter might be able to point me in the right direction please.

Looks like the trv needs replacing. A ten minute job by a plumber/heating engineer. Can you turn the pin with pliers?

Can you get another plastic top from another rad and try that? They are supposed to come off as such. If the second one won't turn, you might be able to turn the rad on a little with by turning the top pin with a pliers. This might keep it stuck 'On' but that might be OK til your mother leaves.
But we just had this exact issue and the plumber had to replace the valve.

Quite easy to refit the bit that came off in your hand. There's a nut at the bottom that engages with the threaded bit on the radiator pipework. Do what this guy is doing at 2:35

please don't use pliers on the pin. It isn't supposed to turn, it is just pushed down by the mechanism in the knob.

yes, the screw collar should hold it. Turn the top knob all the way up before trying to re-fit it (you will find it goes slightly up and down when rotated).