Central Heating Radiator fails to heat up

[tali1]

The radiator in front bedroom is always low on heat (v annoying going into a cold-ish room) -all other radiators are fine
I have bled the radiator in the loft (as this is in highest postion) and it only has a small amount of air.Also all other radiators have no air locks either
To get front bedroom radiator to heat up properly i always have to bleed it and let water out -this i find gets it to heat up
So what is causing this 1 radiator fail to heat up (the valve is set to full)

[Old_Geezer]

It may be that the system isn't balanced properly so all radiators heat up much the same.

Maybe the thermostat is somewhere where it cuts the heat off before the bedroom is warm enough ?

[HowardKennitby]

If you have to bleed it regularly then it seems to me that air is getting in nearby. You need to check connections ahead of this radiator.

[buildersmate]

No, it is not to do with air getting in the system. Folks on this site seem obsessed with believing that radiator bleeding is a necessary and routine operation that is required on CH systems.
The most likely issue is that the system is not balanced properly - meaning that very little hot water finds its way into the faulty rad. It happens because there is too much resistance to water flow into that room because the path the water has to take is the longest length of pipework.
The way you may be able to correct this is to try unscrewing the lockshield valve (at the other end to the valve you say is full on) anticlockwise. Try turning it one quarter turn at a time, then see what effect it has. If this won't work (because it is completely unscrewed already) you will have to ask a heating technician to do it for you (because every lockshield in the house will have to be reset-up).

[jomifl]

Try turning off a couple of rads elsewhere, if the bedroom rad gets warmer it indicates that the system needs balancing.You will need someone who knows what they are doing as buildersmate suggests if you want this resolved quickly.