Fixing a Toilet Ballcock Assembly

The ballcock assembly looks more complicated than it really is. When you go to a hardware or plumbing-supply store to buy a new ballcock assembly, you’ll find that both plastic and metal units are available. Plastic costs less and will not corrode. But plastic assemblies are not as sturdy as metal ones. In addition, plastic units usually cannot be repaired because many of them are sealed. Nevertheless, you can purchase a type of unit different from the one you’re replacing as long as the new assembly has a threaded shank the same size as the old one. If possible, bring the old assembly with you when you to buy the replacement. Here’s how to fix an older-style ballcock assembly:

Step 1: Make sure the water shutoff valve for the toilet is in the OFF position.


On many older ballcock assemblies, a pair of thumbscrews holds the valve plunger. You will have to unscrew them to remove the valve.

Step 2: Remove the valve plunger, and you’ll see on or two washers or O-rings. If any of these parts is faulty, water will flow out past the plunger continuously, and the toilet will run constantly. Examine all of the washers and replace any defective ones.

Step 3: If the ballcock assembly is sealed, replace it as a unit. Shut off the toilet water supply at the shutoff valve and flush the tank. Unscrew the float arm from the old ballcock unit and remove the refill tube from the overflow tube.

Step 4: Look under the tank for a coupling or slip nut where the water inlet pipe enters the base of the tank. Loosen the coupling nut to free the water inlet pipe. Then use an adjustable wrench to grip the retaining nut or locknut immediately above the sip nut under the tank. Use another wrench to grip the base of the ballcock assembly shaft inside the tank.

Step 5: Unscrew the locknut under the tank to remove the ballcock assembly. If the nut is stubborn, use penetrating oil to loosen it.

Step 6: Life the old assembly out of the tank, saving the washers from all connections, both inside and outside the tank. New ones will probably be included with the replacement unit, but keep the old parts until you’ve installed the new ballcock assembly in case new parts are damaged during installation.


When installing a new ballcock assembly, make sure the gasket and the washer are properly seated and firmly secured by the retaining unit.

Step 7: Insert the new ballcock assembly into the hole in the tank. With the inside washer in place, tighten the locknut on the outside sufficiently to make the inside washer fit watertight against the hole, but don’t over-tighten it.

Step 8: Replace the coupling nut and water inlet pipe, reinstall the float arm, and set the refill tube into the overflow tube.

Step 9: Turn the water back on at the toilet shutoff valve and check for leaks at all points. Of course, another thing to check is that the float ball does not rub against the back of the tank.

Newer types of ballcock assemblies eliminate the float arm and the float ball. One kind features a plastic cup that floats up to cut off the water as the tank fills. You can set the water level in the tank by adjusting the position of the plastic cup on a pull rod. One advantage to this type of ballcock assembly is that it lets the water run full-force until the tank is filled. It then shuts the water off immediately, eliminating the groaning noises some toilets make as a float arm gradually closes the valve.


One type of diaphragm-powered valve rests close to the bottom of the tank (left); it eliminates the float ball and float arm. Another type (right) uses a flapper cover, lifted by a chain.

Another type of ballcock also eliminates the float ball and float arm. This is a small unit that rests almost on the bottom of the tank; it’s diaphragm-powered valve senses the level of the water from down there. Moreover, since it requires no tools, this assembly is an easy unit to install. To install these newer ballcock assemblies:

Step 1: Turn off the tank’s water supply shutoff valve. Then flush the toilet to drain the tank. Sponge up any water remaining in the tank before proceeding.

Step 2: Remove the old ballcock assembly, following the procedure outlined above. Slip the parts over the water inlet pipe under the tank in this order: coupling nut, friction washer, cone washer, and retaining or mounting nut.

Step 3: Install the new unit inside the tank, fitting the threaded shank down through the hole over the water supply pipe and making sure the gasket fits into the hole. Start tightening the retaining or the mounting nut under the tank onto the threaded shank: hand-tighten it only. Push the washers into place and hand-tighten the coupling nut under tank; be careful not to over-tighten it.

Step 4: Inside the tank, attach one end of the refill tube to the tank’s overflow pipe and place the other end on the stem of the replacement unit.

Step 5: Open the water supply valve to fill the tank. The water level in the tank can be adjusted by a knob on the new valve unit.