Dual Flush Toilet Not Filling! Solutions for Common Problems

Push-button toilets are now the most popular. Buttons are better than handles for flushing a toilet effectively. The functions inside a toilet tank are crucial because they control the filling. 

If a toilet feels slow, we become worried because a slow toilet is insufficient for removing all the garbage from the toilet bowl. Moreover, 

If you want to repair your slow toilet, you must know the reason for the issue. After that, you can fix the problem by abstaining from highly reliable activities to make your bathroom slow.

Quick Causes:

  • Faulty Fill Valve
  • Damaged Seal
  • Blocked Water Supply Line
  • Clogged Inlet Holes
  • Faulty Float Ball or Float Cup
  • Low Water Pressure
  • Warped or Cracked Toilet Tank
  • Closed or Partially Closed Shut-Off Valve
  • Broken or Disconnected Fill Tube
  • Defective Dual Flush Mechanism

Why is my dual flush toilet slow to fill?

There are several functions in a dual flush toilet. If any process of the bathroom becomes problematic, the toilet will automatically become slow. However, if you do not take it seriously and do not call a plumber to repair the toilet set, it can stop filling.

  • A clogged drainpipeA clogged drainpipe

If you want to get a good flushing system for your toilet, you should keep the drainpipe clear. It becomes clogged for several unconsciousness of the toilet user. Suppose you throw a huge amount of tissue paper inside the toilet bowl, do not clean the toilet regularly, and do not take care of the toilet drainpipe; it can be clogged quickly.


When facing this issue, you must call a plumber and immediately clean the toilet drainpipe. Sometimes, the drainpipe can be damaged. But if you take care of the pipe and clean it regularly, you should not replace it.

  • Low water pressureLow water pressure

Can you imagine how your toilet will be flushed without water pressure? Sufficient water pressure is necessary for efficient flushing. But, if your toilet flushing system can not afford the pressure, the toilet will not be flushed efficiently. 


You have to check whether the water pressure for toilet flushing is okay. You have to change it to be in a better position. 

Sometimes, the water supply from the main line can be disrupted. If you notice it, you have to inform the related institutions immediately. They will send maintenance specialists to solve the issue of your toilet water supply line.

  • A clogged ventA clogged vent

A vent of a toilet has a significant effect on flushing performance. It is essential for the air circulation of the bathroom, and the air controls the toilet’s flushing performance. If debris from outside comes and accumulates inside, it may be clogged. Therefore, the dual flush toilet will stop flushing because a clogged vent significantly affects the toilet. 

How can I clean the clogged vent?

So, whenever you notice that the vent pipe of your toilet is clogged, you must take the essential steps to clean it. You can apply the mixture of vinegar and baking soda. 

First, you must climb on the roof because the vent pipe of a toilet is generally located at the top of the roof. Now, take the mixture and apply it inside the vent pipe. You should also use a specific amount of water. Now, wash the vent pipe inside and remove all the debris. Finally, when the cleaning process is complete, you can check the toilet flushing system again.

  • Hardwater

Hard water is the water that contains a high mineral content. It happens because limescale and calcium build up under the toilet rim. Gradually, the toilet becomes clogged. 


It is very easy to get rid of toilet hard water issues. If you want to keep your toilet safe from hard water to flush the toilet easily, follow the process below. 


  1. i) A quarter cup of borax
  2. ii) Two cups of vinegar

Cleaning process:

First, flush the toilet so no dirt can stay on the bowl. Pour borax into the toilet bowl. Take a toilet brush and rub the toilet surface efficiently. Apply two cups of vinegar and sit for 20 –30 minutes. When you use a toilet brush on the bowl after applying vinegar, you can easily remove all germs from the toilet.

  • Faulty plumbingFaulty plumbing

Almost all significant issues of a toilet are related to faulty plumbing systems. The toilet drainpipe can be clogged, the sewage line can be blocked, or any other matter related to the plumbing system may happen. 


Different plumbing systems can be problematic, including flush mechanism, bowl siphon, refill mechanism, etc. The toilet user must check all functional systems individually and then solve the problem with an efficient plumber.

  • No water supply No water supply

You tried many things to start the toilet flushing again, but did you notice whether your toilet’s water supply is okay? If the water supply is mistakenly stopped, your bathroom will not be flushed, although you cleaned all the ways of water extraction. 

So, turn on the water supply and then check the flushing system again.

  • Fill valve or float adjusting issue.Fill valve or float adjusting issue.

If your toilet’s fill valve is not properly adjusted, your toilet tank will not timely fill up. So, if you notice that your toilet tank is not filling up despite repairing all other issues, you have to check the fill valve. You must properly adjust it or change the fill valve.

  • A bad flapperA bad flapper

If your toilet flapper is not good, your toilet can not flush all the garbage properly. When you flush the bathroom, the flapper drains water from the toilet tank. 


You can easily remove the toilet flapper with your hand. Now, collect a new flapper, and install it inside the toilet bowl. Finally, you can understand the toilet flushing activity when you will flush the toilet again. If all other parts of the toilet are okay, you can use the flushing system again.

  • Failing pumpsFailing pumps

The toilet pump keeps a vital role in maintaining the toilet water pressure correctly. But, when it starts to fail, it is a sign that the toilet tank will stop filling quickly. 


The failing pump issue is difficult to solve in a highrise building. It can not be decrypted if you repair it from the main line because any part of the line can be problematic. So, you must check the flat’s toilet systems and determine which part of the building is difficult according to the water supply. Finally, you will repair the toilet pipe’s leak in a specific part of the building.

  • Debris in the toilet tankDebris in the toilet tank

A clean and clear toilet tank is essential for problem-free flushing. But, many unconscious users need more time to notice the toilet tank’s condition. As a result, the tank does not fill up because of the debris.


Cleaning the tank is the best solution to get rid of this issue. You have to open the toilet tank lid. You can wash it with clean water. If the toilet tank is completely rusted, you must replace it.

  • Faulty toilet bowlFaulty toilet bowl

Every toilet user must clean the toilet bowl timely. Otherwise, it will bear a bad appearance. Sometimes, the toilet bowl leaks, so the toilet tank takes a long time to fill. 


First, remove all debris and dirt from the toilet. Determine which part of the toilet bowl is cracked or broken. If you replace it with a new one, you can easily use the new toilet bowl for years. 

Why does my dual-flush toilet keep running?

The toilet tank not filling – is a significant issue. There are several reasons for a running toilet. First, a higher water level in the toilet flushing system is reliable. 

A nonstop running toilet makes a very bad situation. You can do other essential tasks when your toilet tank is not filling, but you can only go somewhere when your bathroom has continuous running water.

If you notice the issue, you must immediately call a plumber to repair it. He will check the water level and fix it quickly. But, some other issues can be related to the problem, including a broken pipe, toilet tank, unclear or damaged seal, etc.

Frequently Asked Questions (FAQs)

Are dual flush toilets hard to repair?

Yes, dual-flush toilets differ slightly from American standard single-flush toilets. They are designed differently, so the repairing process of the toilet is somewhat different. Even if you know how to repair the parts of American Standard single flush toilets, you will need help finding out the other parts of the dual flush toilet. So, if you are a new user, you have to know the places of all aspects of the toilet carefully. You can also search on Google and browse YouTube to solve the issues.

How long can I use a dual flush valve?

Usually, dual flush valves may last between six and seven years. But, they may wear out before your toilet set. So, your toilet may last for twenty years, but you must change the flush valve quickly.  When water continues to run, you will change the flush valve. Otherwise, you can use it.

How often should I clean my toilet fill valve?

The toilet fill valve will be okay if you clean it once a year. 

If you want to fill your toilet tank to enjoy a perfect flushing toilet, you should clean the toilet fill valve promptly. Therefore, it will be protected and safe. 

How can I clean a clogged fill valve?

A clogged fill valve of a toilet tank is highly responsible for the issue of the toilet tank not filling. If you face a problem, check whether the fill valve is clogged. So, remove the toilet lid cove, hold the fill valve, and turn it counterclockwise to remove it. Now, disassemble the fill valve and then check the inside. If the inside part of the fill valve is clogged, you can easily wash it with soap and water. Turn on the faucet and clean the valve inside with sufficient water flow.

Still, have a question after reading this Dual Flush Toilet Not Filling article? Comment below.

Hi, this is Robert Crossan, the owner of this website, has 17 years of experience in the installation, maintenance, and repair of toilets and plumbing systems. After completing the Level 2 Basic Plumbing course in 2005, I started working in both domestic and commercial buildings as a professional plumber. So I can figure out the core difference between different toilet models and brands. It also helped me monitor their work performance and setbacks.