Cleaning out a rad?

[kev25v6]

Ive got one radiator that never seems to be that hot, especially at the bottom of it. Ive tried turning all but that one off but it still stays the same. Im guessing that it is full of sludge so im looking at removing it and cleaning it out. Ive got a combi for my boiler, if i turn off the pilot and drain down from the lowest rad drain pipe no more water will enter the system unless i open the filling loop, correct?? I dont want to open the pipes to find it still full of water. Is there anything that normally causes trouble with the rad valves, snapping off etc that i need to look out for? It looks like there is some ptfe tape on one joint, is it best to put a new bit on each joint before fastening it back together? Ive got a few towels ready for when the black sludge splashes everywhere. The pipes do seem to angle a bit off of vertical, maybe around 80 degrees but this might just be because of the rad pulling them out of line a bit.

 

[kevplumb]

sounds ok

but it might be just a sticky trv

or the lockshield valve closed to much

 

[kev25v6]

I was wondering that but i can turn it off and it does go completely cold and i removed the dial earlier and gave it a good tap with the pliers just incase it made a difference but it does not. I even shook the rad a bit and gave it a few taps at the bottom to see if it would dislodge anything but no better. The top of it can get quite hot but the bottom is still only warm at most, makes me think it must be sludged up at the bottom of the rad.

 

[kev25v6]

I put a bit of wd40 on the pin under the trv cover to see if it will free the pin up or not, should i be able to just push it down with the side of a screwdriver or should it be quite stiff? If anything it looks to be stuck fully open not closed.