You need to take urgent action if your toilet has been running constantly and causing the toilet bowl to overflow. This article discusses some of the components that you should check to fix the problem.
The Flush Valve
The flush valve opens to let water through when the flush lever is pulled. This valve then closes once the toilet tank is empty. The flush valve can allow water to continue flowing into the toilet in case its rim is damaged (having a crack, for example). The only option for a damaged flush valve is to replace it because such components cannot be repaired.
The Tank Ball
The tank ball sits in the flush valve to prevent water from flowing through to the toilet bowl. A worn or damaged tank ball can fail to do its work, and the toilet will run continuously. Start by turning off the water flow at the shut-off valve found at the back of the toilet. Reach into the toilet tank and feel the tank ball for any defects, such as cracks and loss of shape. Follow the manufacturer's instructions and replace the tank ball with a new one if the current one is damaged or worn.
The Flush Lever
The lever that you pull to flush your toilet can also cause the toilet to run continuously. This can happen when the lever assembly is too loose or very tight. A lever assembly that is too tight may keep the flush valve partially open. This will allow water to keep flowing from the tank to the toilet bowl. Loosen the chain assembly by hand and observe whether water continues running into the bowl. Tighten the chain assembly in case it was too loose and wasn't operating well.
The Fill Valve
Canister-type valves can become clogged with dirt over time. This can prevent them from cutting off the flow of water from the inlet pipe after the toilet has been flushed. Water will then overflow into the toilet bowl through the overflow tube. Remove the cap of the valve and check for any accumulated dirt in the tube. You should then replace any damaged parts, such as the seals and washers.
Call an emergency plumber for help if water is overflowing from the toilet bowl since your problems may include a clog in the toilet drainage system. The plumber will inspect the toilet and find a lasting solution to the problem.