Cold Radiators

Could anyone please give me some help please.
Hot water ok but my radiators are cold [lukewarm in patches sometimes] i've bled the radiators. The pump is running [well humming when switched on] but getting very hot. I'm guessing there is a blockage somewhere, if there is is there something I can put in the tank to cure this totally or will I need to drain the water from the radiator system. If that is the case what is the best way of doing this and then refilling it.
Many thanks for any help
Sandaz
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are you usa or uk? got a gauge on the boiler? how's the fill valve?
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I'm UK, there is no gauge i can see on the boiler, the fill valve looks ok is there a way to check it?
Thanks sandaz

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Have you bled the pump - it sounds as tho it might be dry.
Just remove the big screw in the centre of the pump - you should get a small amount of leakage. If you get some gurling/spitting then its the air coming out. Thru the hole you can check the pump is running. Put the screw back after and mop up the small amount of leakage.
Sandaz wrote:

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