A constantly running toilet is usually a sign that the flapper is not closing properly. Located inside the tank, the toilet flapper allows water to flow into the bowl from the tank. When you press the handle on the toilet, the flapper opens to allow flushing. The flapper closes when you release the handle to allow the tank and bowl to refill. A kinked or broken chain, mineral deposits on the flapper seat and a worn-out flapper can prevent it from completely closing and forming a tight seal.
A kinked chain will prevent the flapper from completely closing. This allows water to continually flow from the tank. Remove the tank lid and set it aside. Look for the chain connected to the toilet handle. Straighten the chain if it has a kink in it, or check to see if the chain is too tight. There is a clip on the chain that can be moved to release tension. If the chain is damaged, the it will need to be replaced.
In hard water areas, mineral deposits such as lime and calcium build up over time. This buildup can be removed by using a lime and calcium remover. Read the instructions on the cleaner to make sure that it is safe for toilets or septic tanks. There is a seat directly underneath the flapper. Drain the water from the tank by shutting the water off. Flush the toilet to drain most of the water from the tank. Lift the flapper to allow more water to flow out of the tank. Squirt the lime and calcium remover on the flapper and the seat. Allow it to set for the recommend time and rinse clean. Refill the tank, and flush to remove the cleaner from the tank. White vinegar will also work if the buildup is not too heavy.
Your flapper is worn out if you have checked the chain and cleaned both the flapper and seat, and it still will not close. Over time the flapper begins to lose its ability to properly seal, and it is time to replace it.
Replacing a Toilet Flapper
Replacing a toilet flapper is a simple task that anyone can do. Shut the water off and flush the toilet. This will make it easier to access and replace the flapper. Disconnect the chain from the arm that leads to the handle. Unhook the ears of the flapper from the fill tube arms. Take the flapper with you to the hardware store so that you purchase an identical replacement. Not all flappers are designed for all toilets. Install the new flapper and turn the water back on. Do not remove links from the chain until you check to see if the flapper is working correctly. If it's too loose, the flapper won't stay open when you press the handle, and if it's too tight, it will not completely close. The only way to accomplish this is by trial and error. Remove excess chain to prevent it from getting tangled with the handle. Put the tank lid back on and you are finished.