If you have a toilet that won't stop running or continues to flush over and over again, then it is because the water in the toilet keeps draining out. This indicates some kind of problem with the toilet. Since higher water level and gravity makes the toilet flush, it is important that the water emptied into the bowl at the end of a flush remains there to keep from losing water and causing toilet malfunction. There are several reasons why your toilet may be draining out water.
Float Ball Position
The float ball inside your toilet's tank is a round balloon like floatation device that is attached to a lever that tells the water valve when to let water in and when to turn it off. If the ball is adjusted to high the water level will climb to the point that the water runs into the overflow pipe causing a constant stream of water into the bowl. This could result in repeated unwanted flushing. The float ball could also be damaged and allow water into it. This will make it ineffective and result in the same problem.
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Flush Valve Problem
The flush valve, also known as the flapper, is the seal that closes to stop the flow of water from leaving the tank and entering the main toilet bowl. If this valve does not seal properly then water will seep into the bowl causing the constant need to refill the tank and continual flushing. Often the cause of a bad seal are mineral deposits around the valve seat. The valve itself could also be damaged.
The toilet handle connects to the float ball through linkage that can sometimes get stuck. if you have ever seen a toilet that will continue to run water unless you wiggle the handle, then it is likely the linkage between the handle and float ball is the problem.
The ballcock assembly is similar to the flush valve, but instead of letting the water out of the tank and into the toilet bowl, the ballcock is responsible for letting the water into to the tank from the supply line. This part may have sediment build up, keeping it from doing its job properly. You can clean out the ballcock or replace it if the assembly seems to be damaged or broken.