Step 1: Check the Overflow Tube Height

The overflow tube is a part of the flush valve assembly. The overflow tube might be too short if the current flush valve assembly isn’t compatible with the toilet. The tube could also have been cut too short during installation. If the overflow tube is too short, causing the water to run continuously, you will need to replace the flush valve assembly with a compatible flush valve. However, if the overflow tube is the right height for the toilet, then the issue might be the water level or the fill valve.

Step 2: Lower the Water Level in the Tank

Ideally, the water level should be set to about an inch below the top of the overflow tube. If the water level is set higher than this, it’s recommended to lower the water level by adjusting the float rod, float cup, or float ball. Float rods and float balls typically extend out from the side of the fill valve, while a float cup is a small cylinder that is attached directly to the fill valve where it slides up and down with the water level.

To adjust the water level, locate the screw that attaches the float to the fill valve and use a screwdriver or a set of channel locks to turn the screw about a quarter-turn counterclockwise. Continue to make quarter-turn adjustments until the float is set to the desired water level. Keep in mind that if water is trapped inside the float, it will sit lower in the water, leaving the fill valve partially open. Correct this issue by replacing the float.

If the water continues running until it flows into the overflow tube, regardless of the float level, then the issue is probably caused by a faulty fill valve. However, if the water is continuously running but not flowing into the overflow tube, then the flush valve might be the problem.

Step 3: Inspect the Flush Valve Chain

The flush valve chain is intended to lift the flapper in response to the toilet lever or flush button being used. If the flush valve chain is too short, the flapper will not be able to close properly, resulting in a steady stream of water constantly flowing through the toilet. Similarly, if the chain is too long, it can get trapped underneath the flapper, preventing it from closing.

Check the flush valve chain to make sure it’s the right length to allow the flapper to fully close without extra links of chain that could become an obstruction. You can shorten the chain by removing several links until it’s the right length, but if the chain is too short you might need to get a replacement flush valve chain to resolve the problem.

Step 4: Check the Flapper

The flapper is typically made of rubber and can become warped, worn, or coated in grime over time. Inspect the flapper for any signs of significant wear, warping, or grime. If the flapper is damaged, replace it with a new flapper. If it’s just dirt, simply clean the flapper with a solution of warm water and vinegar.

Step 5: Replace the Flush Valve

After inspecting the overflow tube, the water level setting, the length of the flush valve chain, and the current state of the flapper, you might find that the problem is caused by the actual flush valve assembly. Purchase a compatible flush valve assembly online or from a local home improvement store to ensure the new overflow tube will be tall enough for the toilet tank.

Start the replacement process by turning off the water to the toilet using the isolation valve on the water inlet line. Next, flush the toilet to drain the water and use a cloth, towel, or sponge to remove any remaining water from the tank. Disconnect the water supply to the tank using a set of channel locks.

You need to detach the toilet tank from the toilet bowl to remove the old flush valve assembly. Remove the tank-to-bowl bolts and carefully lift the tank off the toilet to access the toilet-to-bowl gasket. Loosen the flush valve nut and remove the old flush valve assembly, setting it aside in a nearby sink or bucket.

Install the new flush valve in its place, then tighten the flush valve nut and replace the tank-to-bowl gasket before putting the tank back into position. Secure the tank-to-bowl bolts and reconnect the water supply to the toilet. Turn the water back on and allow the tank to fill up. While it’s filling, take the time to check for any leaks at the base of the tank. If the water continues to run after the tank is full, then the tank-to-bowl gasket or the flapper might be improperly installed.

How to Shut Off Water
Step 6: Replace the Fill Valve

If you find that the overflow tube is the right height for the toilet and the water level is set about an inch below the overflow tube, but water continues to flow into the overflow tube, the issue is likely the fill valve. Replacing the fill valve isn’t as difficult as dealing with a faulty flush valve.

Turn off the water to the toilet using the isolation valve on the water inlet line, then flush the toilet to empty the tank. Use a cloth, towel, or sponge to soak up any remaining water, then remove the water supply line with a set of channel locks. Unscrew the locking nut on the bottom of the tank to loosen the fill valve assembly.

Remove the old fill valve assembly and set it aside in a sink or bucket, then install the new fill valve assembly. Adjust the height of the fill valve and float to ensure it sits at the correct level for the toilet. Secure the fill valve assembly with the locking nut on the bottom of the tank. With the new fill valve in place, reattach the water supply line and turn the water back on. Check the bottom of the tank and the water supply line for leaks as the tank fills with water. If the repair was successful, the water will stop flowing into the tank when the float reaches the set level instead of continuing to fill until it spills into the overflow tube.