My cold water tap to the bath is fed from a tank in the loft but the sink tap is mains fed. I found that the bath tap flowed to a trickle when it had been used a lot and assumed it was silt from the bottom of the tank. I managed to restore the flow by using a compressor to back flush the pipe from the tap end, resulting in limescale being pushed back up into the header tank. BEWARE too much pressure could result in burst pipes especially if they are well blocked.
John M, January 2010