Check the cold water storage tank in the loft (or certainly somewhere higher than the hot water cylinder). It may be that debris has come through from this tank, especially if you've drawn off a lot of hot water in a short time. If you do find a lot of debris in the tank, turn off your main stopcock, then open a hot water tap and run it until it stops. The cold water storage tank will then be empty so that you can clean it out.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!