Okay it might seem a bit odd but I do do a bit of DIY from time to time (I'm pretty sure my wife will be sniggering at this comment). One of my last projects was replacing the washer on a tap which is a simple enough task on its own provided that tap actually as a stop cock under the basin. Unfortunately this was the hot water tap and there were no stop cocks to be found and it left me with the laborious task of turning off the hot water cylinder and also the mains water that filled the refill cylinder on the roof (this is the one all the cold water taps in your house come off except the kitchen which should come off the mains) and then draining the hot water cylinder into the bath which took almost an hour.
Once I was happy there was no water left in the system I took apart the tap and replaced the washer put the tap back together again and turned on the mains water supply again. This took about another hour to fill up properly until I didn't hear the water running anymore I then turned on the taps to get all the air out of the system but no matter how long I ran the taps for, the tap with the washer I just replaced wouldn't give out any water. It left me annoyed because I'd probably have to do the whole damn thing over again, some how there was a trapped air bubble in the system which was stopping the flow of water, what to do?
Well its pretty simple actually, all I did was take a garden hose from outside and send water up the tap for a couple of minutes and like magic the air bubble was gone and the tap flowed again!