Hot at the top, Cold on the bottom

I have a problem with my radiators.
They're Hot at the top, Cold on the bottom (Therefore it isn't air, which would cause the top of the radiator to be cold & the bottom hot) I've blead the radiators, and they are all filled with water.
Does anyone have any ideas?
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Circulator bad?

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When was the last time you flushed them? I am no expert but my grandmother used to bleed each tank just before the heating season. They were large cast iron radiators, we used to fill up a BIG kettle 5 times at each tank.
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One of the most interesting sites I've ever seen is www.heatinghelp.com , all about hot water and steam heat. Read through there and see if there isn't an answer.

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