Dual Flush Toilet Running Constantly. How To Fix It?

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Last Updated on September 6, 2022 by acechapman

A dual flush toilet with a constant running flush will indicate that the dual flush valve seal may be worn, warped, or dirty. You could also have a defective fill valve that is constantly filling the tank of your toilet.

If the toilet fill valve is causing the problem, it will continue to fill the tank with water. This water will then flow down through the overflow tube to the bowl. This could be the reason your toilet doesn’t stop working.

The toilet fill valve is a part of the toilet tank located on the left-hand side. It connects from under the toilet tank to the water supply line. Its function is to refill the toilet tank after flushing.

Dual flush toilets have a float cup/cylinder that is attached to the vertical body of the fill valve. It controls the opening and closing of fill valves as well as the water level in the tank.

What causes a dual flush toilet that is running constantly?

The float of the toilet moves down to the bottom and the fill valve which was closed until then opens. As the tank fills, the float rises gradually to the set height, where it will stop, and the fill valve will then close. The toilet tank’s water level should be approximately 1/2 inch below its overflow tube.

If the height of your toilet float exceeds the recommended setting, the fill valve will continue to fill the tank with water. The excess water will then run down to the bowl via the overflow tube.

The fill valve may also be defective, in that it does not close even when the tank is full. The fill valve will continue to fill the tank with water and will need replacement.

The overflow tube is the large pipe that runs through the middle of the tank. It then sends any excess water back into the bowl to prevent overflowing the toilet.

dual flush toilet running


Before you attempt to fix a running toilet, make sure that the issue is not with the fill valve. You can do this by removing the lid from the toilet tank and placing it in a safe location where it will not fall or crack.

The tank’s water level should be checked relative to the overflow pipe. If water is flowing through the tube, then it’s likely that the fill valve or the toilet float is the problem.

The height of the toilet float can be adjusted easily, but a faulty or leaky fill valve must be replaced. Toilet floats can be adjusted and new fill valves sold together.

The problem is most likely the toilet seal if the problem doesn’t seem to be with the fill valve/float.


You may need to replace parts of the dual flush toilet in order to fix a running toilet if they are damaged or misaligned. You will need to replace the seal if it becomes hardened or worn over time.


The problem with a dual flush toilet is usually the seal. Let’s see how to replace or fix a dual flush toilet seal.

  • Turn off the water supply for the toilet. The shutoff valve for the toilet is located on the wall just behind the toilet. Turn the valve clockwise.
  • To drain as much water from the tank as possible, flush the toilet.
  • Then, take off the lid from the toilet tank and store it in a safe location.
  • To remove the dual flush valve body, hold it in your hand and turn it clockwise or counterclockwise.
  • Then, check to see if the seal has become worn or misaligned.
  • You will need to replace it if it becomes worn or hardened. It is made from rubber, so it is elastic. Take it out and replace it with the new one.
  • If the seal looks dirty, you can clean it with running tap water. Make sure to clean the opening of the flush valve where the seal is located.
  • If the seal is not aligned properly, you can straighten it. You can also use Vaseline to seal it.
  • As you took it out, put it back and align the flush buttons exactly as before.
  • Turn on the water supply to your toilet, and allow the tank to fill.
  • Pay attention to any water coming into the toilet bowl.
  • Place a piece of tissue paper on the toilet rim to check if it is dry.
  • Once you are satisfied with the results, put the lid on the toilet tank and flush it a few times to confirm that everything is working properly.


This is how to fix a dual flush that isn’t working because there is too much water in the tank

  • Turn off the water supply to the toilet, and flush it.
  • Then, place the lid on the toilet tank and remove it.
  • You will find a long, plastic screw alongside the toilet float. This screw adjusts the height of your float cup and the water level within the tank.
  • To turn the screw counterclockwise, use your hands or a screwdriver.
  • Notice the change in the water level at the toilet by opening the water supply. It should be approximately 1-1/2 inches below the overflow tube.
  • You can then adjust the screw to achieve the desired height.
  • Try flushing the toilet several times to see if it returns to its original height.
  • Finally, reattach the lid back to your toilet tank.
dual flush toilet running

Replace the Fill Valve

The fill valve may be faulty, which is another reason homeowners experience problems with their toilets flushing constantly.

Although it is possible to repair your fill valve, it can be difficult. Sometimes it is difficult to locate the parts you need without purchasing a complete new kit.

You can easily purchase new fill valves and are affordable. It could be that replacing an old fill valve might prove more trouble than it is worth. It is better to replace the fill valve than repair it.

What You Will Need

  • Kit for filling the toilet
  • Adjustable wrench
  • Towel
  • A small bucket
  • Screwdriver


  • Turn off the water supply for the toilet.
  • To remove as much water as possible, press and hold down the dual flush button.
  • Then, take the lid off the toilet tank.
  • Take out the float in the toilet.
  • Use a towel to remove excess water from the toilet tank.
  • Place the bucket under the fill valve. This will catch any water from the toilet tank.
  • Use an adjustable wrench to take out the mounting bolt on the side.
  • Then, pull on the valve to remove it from the tank.
  • Prepare the new fill valve and adjust its height so that it is at least 1″ above the overflow tube.
  • Push the bottom of your valve into the opening in the toilet. The valve should be flush with the tank’s floor.
  • Lock the bolt on the outside of your toilet. To tighten the locking nut, use a wrench.
  • Attach the refill tube and the overflow pipe. Here you can also use your wrench.
  • Then, attach the fill valve.
  • Turn on the water supply. Wait for the tank to fill.
  • To ensure that the fill valve works properly, flush the toilet several times.

Wrapping up

We are concerned if the dual flush toilet doesn’t stop draining. It doesn’t need to be difficult to fix, as you’ve learned from the three methods described in this article. We are sure that the step-by-step instructions will have helped you get your toilet working again.

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