When a ballcock is stuck, it will cause an overflowing toilet cistern and lead to inefficient water usage. Luckily, it is a simple and inexpensive problem to fix. The ballcock consists of an arm attached to a plastic float. As the water rises and pushes up the float, a valve on the other end of the arm shuts off the supply when it gets to a certain point. A ballcock can get stuck when it rubs against other items, gets clogged with dirt, rust or lime build-up, or is damaged.
Step 1 - Turn off the Water
Turn off the water supply to the toilet, or to the whole house if you don’t have easy access to the toilet water supply. The valve is usually located below, or to the side of the cistern. On a roof tank, you should find the tap on the top pipe.
Make sure the water is turned off by taking off the lid of the cistern or tank, and pushing down on the ballcock arm. There should be no water gushing out. Before you go any further, check that there is no water in the ballcock float. You can unscrew the float counter clockwise, and shake it. If you hear water sloshing around you will need to replace it.
Step 2 - Remove the Arm
If the float is intact with no water in it, undo the nut and the backnut. This backnut is what holds the valve in position in the tank. You will see a split pin that holds the arm in place. Take out this pin and the arm will now drop out. If the pin is hard to remove, you will need to twist and pull it while squashing the ends together. You can use pliers to make this easier.
There is a cap at the end of the ballcock barrel; remove it and hold the threaded part up. Tap this until the washer drops out. There may or may not be a holding cap on the ballcock washer. If there is a cap, and it is threaded, turn it counter clockwise. Dig out the washer with a screwdriver if there is no cap. Then, you will need to replace the washer.
Step 3 - Put it Back Together
Screw back the washer cap and slide the washer barrel into the ballcock, making sure the hole in the barrel is at the bottom. The washer side goes in first. Wriggle the arm back into the ballcock barrel and line up the holes for the split pin. Put in the split pin and separate the ends slightly so it will not creep out.
Place the ballcock back into the tank and replace the backnut loosely. Tighten the nut clockwise after lining up the pipe. Turn on the water and check for leaks. If the level of the water is too high, bend down the arm a little so the water shuts off at a lower level. If the water level is too low, bend the arm in an upward position.