Airblock in cold water pipes

[States]

Hope someone can help. The cold water pipes in the upstairs of the house have an air block. This has happened before and a plumber has sloved the problems but I can't recall how he did it.

If too much cold water is used at once, the tank does not have time to fill up at the same rate and air gets into the pipes.

The plumber had some simple way of unblocking it by unscrewing the tap and creating a vaccum somehow by putting his hand over the hole where the tap was.
anyone know how this works?

 

[davidoco]

another way (apart from the hand over the tap method!) is to fit a hose to your kitchen tap and run that up to the bathroom, hold it as best you can on the tap and turn on the kitchen tap. That will blow/push the air back up into the header tank. Not a recommended method for hot water taps.