Cental Heating Air Lock

I think I must have an air lock in my central heating system, it consists of a wall mounted boiler, cold water tank and header tank in the loft, the water pump is in the airing cupboard next to the hot water tank, the pump straed making a noise and the radiators were only getting warm at the bottom, I tried to bleed them without any luck so i removed the pump which is only 2 years old, it was completley dry inside. Any idea's how to remove the air lock?
Zetor
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In an earlier contribution to this discussion,

Check the small fill/expansion tank in the attic. Make sure that the ball valve is working. It may have stuck, and all the water evaporated and not been replaced. If there is a tap or gate valve in the feed pipe from the fill-expansion tank to the system, make sure that it is turned on!
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Cheers,
Set Square
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On Sun, 25 Jan 2004 21:12:43 +0000, Set Square wrote:

If the pump has not been written off by being run dry.... To get the air out of the [new 8-(] pump undo the chromed disc or black plastic knob on the end of the pump motor body which should let out air and a few dribbles of water.
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Ed Sirett - Property maintainer and registered gas fitter.
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