How to Fix a Toilet That Keeps Running

How to Adjust or Replace an Overflow Tube

The overflow tube, a hollow tube connected to the flush valve, prevents the toilet tank from overflowing if the fill valve does not turn off.

1. Check the Water Level

   Remove the tank lid and check if the water level is too high, causing it to run into the overflow tube. If it is, the water level should be lowered.

   If the water is not running into the overflow tube, then the issue is likely with the flush valve.

2. Adjust the Float Rod or Float Cup

   Adjust the float rod or float cup to lower the water level inside the toilet tank. A float rod is a horizontal rod extending from the fill valve to the float ball. A float cup is a small cylinder that wraps around the fill valve and slides up or down with the water level.

   Use a screwdriver, a set of channel locks, or pliers to turn the adjustment screw about a quarter-turn counterclockwise to lower the water level. Adjust until the water no longer flows into the overflow tube.

3. Verify the Overflow Tube Height

   If the overflow tube is too short, water will continuously flow into the tank and out of the overflow tube. To fix this, replace the flush valve. The new flush valve must be compatible with the toilet.

How to Replace a Toilet Flush Valve

The flush valve is an assembly within the toilet that consists of an overflow tube, tank-to-bowl hardware, a tank-to-bowl gasket, a flapper, and a chain that connects to the flapper. The main purpose of a flush valve is to open the flapper to allow water to flow into the toilet bowl when the toilet is flushed and to close the flapper when the toilet tank is empty to allow the toilet tank to refill.

1. Inspect the Chain

   Verify that the chain is the right length to allow the flapper to fully close and open without extra chain. If the chain is too short, it won't allow the flapper to close properly. If the chain is too long, it may get trapped underneath the flapper, causing it to leak.

2. Inspect the Flapper

   Turn off the toilet's water supply and drain the tank. Inspect the flapper at the bottom. If it is dirty or slimy, soak it in white vinegar and rinse with clean water. If it is warped or worn, replace it.

3. Remove the Flush Valve

   Turn off the water to the toilet. Drain the toilet tank by flushing the toilet. Use a cloth or towel to dry up any remaining water before disconnecting the water supply to the tank with a set of channel locks.

   Disconnect the flapper and remove the tank-to-bowl bolts to remove the old flush valve. Lift the tank off the toilet to access the toilet-to-bowl gasket. Loosen the flush valve nut.

4. Install the Valve

   Install the new flush valve. Tighten the flush valve nut. Replace the tank-to-bowl gasket. Carefully put the tank back into place and reinstall the tank-to-bowl hardware.

5. Test the Toilet

   Reconnect the water supply to the toilet and turn the water back on.

   Check for leaks at the tank's base to avoid accidental water damage. Flush the toilet to test the new flush valve and verify that the toilet stops running with the new part installed by allowing the toilet to fill up.

   If the water keeps running, the tank-to-bowl gasket or the flapper may not be properly installed.

How to Replace a Toilet Fill Valve

The fill valve controls water flow into the tank from the main water supply. Replacing the fill valve isn't as difficult as replacing the flush valve, though you will still need a set of channel locks and a cloth, towel, or sponge.

1. Verify the Fill Valve is Faulty

   Remove the top of the toilet tank and check the set water level and the height of the overflow tube.

   If the overflow tube is an appropriate height for the toilet and the water level is set to about an inch below the top of the overflow tube—yet the water continuously flows into it—the problem is with the fill valve.

2. Turn off Water and Drain Tank

   Turn the water off to the toilet with the isolation valve on the water inlet line. Drain the tank by flushing the toilet. Soak up excess water with a cloth. Finally, remove the water supply line by hand or, if it is tight, use a set of channel lock pliers.
   

3. Unscrew and Remove Assembly

   Unscrew the locking nut on the tank's bottom and pull the fill valve assembly out. Place the old fill valve in a sink or bucket to catch excess water.

4. Insert and Adjust New Fill Valve

   Adjust the height of the new fill valve to suit the specific toilet tank and the desired water level. Insert the threaded end of the valve into the bottom of the tank. Secure it to the tank with a locking nut to create a watertight seal. 

5. Reconnect Water and Test

   Reconnect the water supply and turn the water on. If the replacement was successful, the fill valve will immediately begin filling the toilet tank with water and will stop when the float arm or float cup reaches the set level.

When to Call a Professional

If the water is overflowing or close to the rim of the toilet bowl while the water is running, or after you have fixed what you thought was wrong, you may want to turn off the water valve to the toilet and call a plumber. It may mean an additional clog or another issue with the toilet.