Air in a single radiator

[Kewat66]

Hi all,
I have just serviced a Worcester green star 30 CTI system boiler and the customer has asked me to look at the central heating system. one radiator on the system is constantly being bled?
All the other rads get piping hot no issues with the heat just this one radiator? It is upstairs in a bedroom underneath the loft where the cylinder is. I cant see any leaks on the system or see anywhere that air maybe getting into the pipe work.
any thoughts?

thanks
kewat66​

 

[Ch4 plumbing]

Check all the rad valves are tightened up fully, the system can pull air on and not let water out.

 

[Bagsy]

Hydrogen or air ? Worth checking, to decided what way the diagnosis will take,

 

[Kewat66]

Just found out the system was cleanned a few weeks ago so i am assuming it wasnt flush through properly and more than likely hydrogen. I will re clean and see what i get.
Thanks
kewat66