one rad wont go off

got a new extension built, guest studio for parents, sys is a combi. got 3 rads up there, shower etc. now in sitting room rad wont go off but that in shower and bedroom is fine. could it be the thermostate? please help, its hot!!!!!!!!!!

Thanks

probably

The radiator must have two valves, one being a lockshield type which is to balance the radiator.
The other valve will be either a lockshield type that you use in an ON/OFF mode. Or a thermostatic valve that automatically adjusts the temperature
to within a degree or so to the setting.
If you have two lockshields, then closing the one without knob a little, will restrict flow and lower the temperature.
If you have a TRV you should be able to turn the setting down, I believe though that some have pins/ keys to restrict the amount of movement and you may have slide these up/down if you can't get valve to close.
So it's a matter of closing or restricting the flow and it must be easily achieveable

Thanks the lockshield did it!
Thank you.