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In order to stop a running toilet, you must first identify the location of the problem. A running toilet is almost always caused by either the flapper or the fill valve, which are both located inside of the toilet tank. You will need to inspect the flapper by moving it in an up and down motion to determine if the sound of running water stops. If the flapper is working properly, you will need to raise the fill valve float slightly to find out if this stops the water from running. If either of these components is causing the toilet to run, it will need to be replaced.
If the running toilet is being caused by the fill valve, your best course of action will probably be to replace the entire mechanism. You will need to obtain a new valve at a hardware store before beginning the job. If your toilet is equipped with a ball cock type of fill valve, you should consider replacing it with a float cup type which typically lasts longer. Before replacing the fill valve, remember to turn off the water supply and flush as much water from the tank as possible. Always follow the manufacturer’s instructions carefully to avoid creating any additional problems.
A running toilet may also be caused by a worn or deformed flapper. This device is typically located at the bottom of the tank and opens when the toilet is flushed to release the water stored in the tank. Although it is possible to replace the flapper without shutting off the water supply or draining the tank, the job will probably be much easier if you do. Most flappers have two flexible rubber ears that attach to the toilet bowl fill tube although some models employ a more complicated clamping mechanism. The more expensive, plastic reinforced models usually last much longer than the ordinary rubber type.
If your running toilet problem persists after you have replaced the fill valve or flapper, you should check to see if the chain connecting the flusher handle to the flapper is becoming caught anywhere. An excessively long chain that becomes trapped underneath the flapper will need to be shortened in order to correct the problem. If this is not the case, you should make sure that the top of the toilet bowl fill tube rises above the highest water level in the tank. If the water level is too high, you will need to adjust the fill valve float mechanism to achieve the correct height in the tank. The correct water level is typically marked on both the tank and the toilet bowl fill tube.