One rad only getting slightly warm

[Helptav]

Hi all. I wonder if you can help please. I have recently bought a 17 year old 2 bed new build. It has a combi in the kitchen which I've just had serviced all ok. I've tried the heating recently all get piping hot apart from the main one (largest In the sitting room) the valve and pipe are really hot but the rad is hardly showing any heat. I've looked at the pin on the trv and seems to move up and down. I even tried to slacken the lock shield valve plus tried bleeding it (was no air) it's like a new rad... Any ideas please ? (Could it be that last one on the run just takes a while as only tested for half hour (all the others piping hot) thanks Paul

 

[JohnD]

Turn off all the hot ones.

Yes, ALL.

Does the cool one now get hot?

Is there a room thermostat in one of the rooms?

 

[Helptav]

I'll try that next time (it's a property I'm doing up so not there) the room stat display is currently broken (plumber meant to be sorting it but brought the wrong one) the room Stat is in the hall way (next room)