The taps that are on sale today are fitted with things called ceramic discs to control the water flow rate. These discs are very tough and dont need to be maintained. Of course nothing is usually bullet proof and a failure can occur, in which case the chances are that it will be the disc. These ceramic discs incorporate two holes in both so that when the tap is turned on, one moves and the other stays still. Once these holes line up, the water can flow. Causes:There might be a problem with the hole alignment, which can be down to small amounts of debris present in the fitting. Mechanical failure may also be the culprit. East London Plumbers can fit new ceramic disc cartridges.The discs can only be replaced, not repaired.The discs what is called handed which means that there is a right on and a left one, so they must not be fitted incorrectly.Inspection and Replacement:1). The first thing to do is to isolate the hot and cold water feeds and drain the water by opening the taps. Take off the heads of the taps. These should be a push on fit or you might need to use a screwdriver to remove the holding screw. 2). Keeping the tap body still, so that when you turn the mechanism it does not move also. Once the mechanism is accessible you will be able to see the actual cartridge.Should you not be confident to carry out this task you must call a professional tradesman like an East London Plumber who is trained to carry out the work.3). Remove the cartridge complete. Visually inspect for debris that may have caused the failure. If no debris or obvious damage is visible, then replace the whole unit with a new one. A good idea is to inspect the seal as well.If necessary, fit a new seal. Re-fit the tap, restore the water supplies and inspect for any leaks.