I've no doubt it is an airlock. To remove air lock fix a hose pipe or similar from the hot tap or any other nearby tap to the cold tap.
turn on cold tap then turn on hot or other tap the water will go up through the cold tap to the tank blowing the air out. Turn off the other tap remove the pipe from the cold tap see how the water runs, it will sputter out a bit then runs smooth. If still slow try again.
Bob, September 2010
