If your tap will no longer open or close then it is probably due to a faulty head gear. The head gear is the part of the tap that lifts the sealing washer away from the seat and enables water to flow through the tap. If the tap will no longer open or close then you can buy a replacement head gear or you can get a tap reviver kit.
This is a tap reviver type kit. It consists of two brand new tap handles and comes complete with new head gears.
This kit is especially useful as it contains two reducing rings and so the head gear can fit three different size taps.
The components are as follows-
1.Cap 2.Retaining screw 3.Handle 4.Head gear 5.Reducing ring 6.Reducing ring
The first thing we need to do is to isolate the water supply to the tap. This can be done by turning the isolating valve beneath the tap (if there is one) or you will have to isolate the water supply to the whole house as described here- Isolate the water supply
For the regular basing tap a small flat screwdriver is required, gently slide this underneath the tap cover and lift off the cover.
Now the screw that holds the handle onto the spindle is exposed it can be removed by turning it anti-clockwise. Once the screw is removed the handle will lift clear.
Using either a correct sized spanner or an adjustable spanner undo the head gear nut, this is never easy. Hold the tap with your other hand to prevent it from moving. If it is really stubborn then try spraying some penetrating oil onto the joint. The head gear will unscrew anti-clockwise.
If the tap is moving when trying to undo the head gear you can wrap cardboard around the tap spout and slide a box spanner over the spout to get more leverage.
This is the old head gear that has been removed, you can see that it is not in very good condition and needed replacing.
You can now check the seat inside of the tap to ensure that it is not damaged, once you have done this you can screw the new head gear into place and then tighten it using the spanner, ensure the tap is in the open position when you re-assemble it so that any debris will be flushed out of the tap and not damage the washer. Fit the new handle to the head gear then the retaining screw and then the cap.
Restore the water supply slowly and water should flow from the tap, after a few seconds you can close the tap.
Here are the taps with the new head gear and handles fitted.