Cold Rads

Hi
I've got one rad thats not heating up. Its on the bottom floor, in a system about 30 years old, no TRV. The others are fine. I've twiddlded both valves to check they're open, but there is nothing more than very slight warmth coming through, while other rads heat up.
There was no air in it btw, what dribbled out looked dark.
What might it be? I've heard about sludge, but there is no cold in the middle at the bottom and hot at the ends pattern, its just almost cold full stop.
Thanks.
Regards, NT
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Sounds like an air lock somewhere in the feed to it. Does this drop down to it from the floor above?
Try to get it going by turning off all the other rads and turning the pump up to max speed. Once you get circulation going again, it should keep going even when you turn the other rads back on.
Roger
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Did this radiator used to get hot, or has it always been cold? We had a similar problem and re-balancing the radiators solved it. Basically, it was the futhest radiator from the boiler, and the closest radiators had their valves open too much. The result was that the restistance of the pipework to the furthest radiator was too great compared to the resistance through the closer radiators - end result, the hot water took the path of least resistance and promptly took a short cut back to the boiler. Closing the radiator valves on the rads closest the boiler increased the resistance there, making the further radiators seem a nicer choice (ie. easier).
I did it using clip on thermometers and the thermostat up full - but you can probably do it roughly by closing the rads (lockshield vavle) closest the boiler and opening them the smallest amount necessary to make it hot enough. Repeat for all rads which are nice and hot and hopefully you should find your cold rad get hotter.
Oh, a quick check to see if this is the problem is to just turn off (via normal vavle) the other radiators. If the cold one gets hotter, then its probably balancing. If it doesn't get hotter - then its something else.
D
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Thanks David and Roger.
The rad is the furthest from the boiler, and it used to get hot, but not this year. The system was way out of balance, so I'll turn the pump to max first and see what happens, since thats easiest, then turn other rads down and hope it works.
Thanks, NT
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