Draining a radiator

[PiKe]

I have a small radiator that I want to drain so that I can add cleaner to my closed loop system. I have closed both valves isolate the radiator. The radiator has a drain off valve on the lock shield side which a radiator bleed key appears to fit on to but when I try to turn it, the key appears a fraction big as it 'skips'.

I can't get pliers on it as it's recessed in a circular section. Any ideas?

 

[PiKe]

So I had another go at this over lunchtime, turns out the valves at either end aren't holding, I slackened off the nut on the valve to the radiator and a fair bit of water came out, undid the bleed at the top expecting no pressure but it squirted out, as I was running out of time, I did everything back up and re-pressurised the system.

 

[PiKe]

Are you absolutely sure that you have closed the valves properly?

Seems like a basic question but I would be surprised if the valves are broken as they are generally very basic. If they are broken you will need to drain the system.

I turned the lockshield, clockwise with grips and screwed the other end clockwise, so yes, I'm sure.