Do you mean that the large tank in the loft is actually empty? If so, the hot water will fail soon as well as the cold - but often the cold is supplied direct from the water mains. Anyway, no matter. In the loft tank you'll see a float valve with a plastic ball on the end. Work this gently up and down a few times and see if the flow restarts. If it does, it will be furred up and its best to replace it. If nothing happens, then it definitely needs replacing!
John, September 2009
