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Fixing A Dual Flush Toilet That Constantly Runs: How To Guide

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Did you know that there are a variety of toilets out there?

From single flush toilets to the more illustrious gravity flush toilets, your basic bathroom needs have never come with such luxury. 

One type of toilet is the dual flush style. This is simply a variation of a standard flush model, but comes with two buttons or a handle, so you can flush different amounts of water.

As with any toilet, issues can arise, though. 

One of the most common problems with dual flush toilets is that they constantly run water.

Not only can this see your water bills increase, but the sound of a steady stream of water flowing in your bathroom can drive you up the wall! Thankfully, there are ways to fix this.

One of the most frequent causes of continuous water in your dual flush toilet is a dirty or warped valve seal.

This can lead to the seal not working properly, allowing water to run.

Another reason could be that the valve has become defective, so water continues to fill the toilet tank

Basically, if your toilet fill valve has an issue, the tank will continue filling up with water.

This will then flow into the toilet bowl via an overflow tube.

When it comes to dual flush toilets, you will typically find a cylinder or float cup installed vertically on the fill valve’s body.

This float cup helps to control the opening and closure of the fill valve, controlling the level of water in the tank.

To find the fill valve, it will usually be on the tank’s left-hand side and connected from underneath.

To fix constantly running water in your dual flush toilet, read on.

We have compiled an in-depth guide to help you recognize why it may be overflowing and ways to combat this. 

Main Reasons For Constant Running Water In Dual Flush Toilets

Fixing A Dual Flush Toilet That Constantly Runs: How To Guide

Dual flush toilets are an excellent choice to help you save water and help do your part in being more environmentally friendly. But, problems can occur.

If you find that the tank is constantly filling up, even after it should have finished, you need to check for the root cause.

Here are some of the most common reasons behind this issue:

Seal Or Flapper Problem

This is probably the number one reason behind flowing water in dual flush and standard flush toilets.

Over a period of time, the flapper (a rubber piece) can become weaker, damaged, or it can simply move out of alignment. 

To see whether this is the culprit, switch off the water supply. Then, flush the toilet, so no water is left inside the tank.

If any water remains, remove it with a towel or a sponge. Next, take the flush valve canister off. This will allow you to reach the seal.

When you have located the seal, inspect it for any signs of cracks or damage.

If there are any traces of this, you will need to buy a new one. You can find different seals online or in your local hardware store. 

If you can not see any sign of damage, check if it has become misaligned.

See if you can realign it, so it sits properly in place.

You could try using some Vaseline on the seal. This can help it function correctly again, at least for some time. 

Here’s an in-depth rundown of how to replace the toilet seal:

  1. Turn off the water flow to the toilet. 
  2. Find the toilet shut off valve on the wall behind the toilet. Rotate this clockwise.
  3. Flush your toilet and keep the flush lever down to remove most of the water in the tank.
  4. Take the tank lid off and put it somewhere safe and secure. 
  5. Grab the flush valve tightly and turn it either clockwise or counterclockwise to remove easily. 
  6. Check if the seal has become worn, covered in debris, or misaligned.
  7. If worn, take it out and replace it with a new one. If it’s dirty, clean with running water from the sink. Also, clean the flush valve opening. If misaligned, try and straighten it. Remember, you can use Vaseline if needed. 
  8. Next, place the valve back and make sure the flush buttons are aligned as before.
  9. Switch off the water supply and allow the tank to fill up.
  10. Look and listen for any water flowing into the toilet bowl. You can hold a piece of toilet paper against the rim of the toilet to see if it stays dry.
  11. If everything seems to be working correctly, place the toilet lid back on and flush the toilet a few more times. 

Zip Tie Is Broken

Yep, the majority of dual flush toilets have a zip tie installed in the fill valve.

This is in place to ensure the bottom of the fill valve is kept in place securely.

If this valve is not secured properly, the toilet may start to run excess water.

After some time, these zip ties can become brittle and break. If this is the case, you just need to replace the zip tie with a fresh one.

On some toilets, you can install two zip ties on the fill valve. This ensures that the valve’s base remains secure and, therefore, doesn’t leak. 

Debris Build Up

The third common reason behind running water in your toilet is excess debris.

To put it simply, you may just need to give your toilet a thorough spring-clean!

Sometimes, dirt and dust can make its way into the toilet, leading to the fill valve malfunctioning. 

To check if dirt is the cause, switch off your water supply and take off the fill valve’s lid.

Look inside for any dirt and debris. If there is any, simply remove it. Sometimes, however, the debris can be very small.

If so, grab a small brush and start brushing out the valve.

Once you have made sure the fill valve is spotless, recap the valve and see if the issue has been resolved. 

If your dual flush toilet (see also ‘What Is Automatic Toilet Flusher And How Does It Work?’) is constantly running water, the fix can usually be pretty straightforward.

In fact, most homeowners can check for the source of the problem and fix it themselves. 

Nevertheless, this may not always be possible.

If you can not find the reason behind the flowing water or are unable to fix it yourself, you should hire a professional plumber.

They will easily be able to find the cause, troubleshoot it, and repair the toilet, so it never happens again. Just bear in mind that this will cost you some extra dollars. 

Adjusting A Dual Flush Toilet’s Water Level

Adjusting A Dual Flush Toilet’s Water Level

If there is too much water in the toilet’s tank, you will need to adjust the water level. Here’s how to do just that: 

  1. Switch off your water supply and flow to the toilet.
  2. Flush the toilet to remove all or most of the water.
  3. Remove the tank lid and place it on the ground safely (preferably on a towel and away from children or pets).
  4. Next to the toilet float, you should find a plastic screw. This allows you to adjust the float cup’s height and the tank’s water level.
  5. Turn this screw counterclockwise using a screwdriver or your hand.
  6. Turn the water supply back on and check the level of water in the tank. Ideally, it should be around 1 to 1 ½ inches below the toilet’s overflow tube. 
  7. If the height isn’t quite right, simply adjust the screw until it is correct.
  8. Finally, flush the toilet a few times to see if the water reached its set height every time. If so, place the toilet lid back on.

In Summary

Dual flush toilets are typically a great investment. But, that doesn’t mean they don’t come with issues.

We hope our guide has helped you solve the problem with constant water running in your toilet.

Remember, if you can not fix the problem by yourself, call a professional plumber. 

Thanks for reading!  

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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