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Why Is My Toilet Tank Overfilling [Reasons & Solution]

The toilet tank is more susceptible to any plumbing issues. Overfilling problems are the most common and crucial among those.

So, why is my toilet tank overfilling? Mainly, this problem occurs due to a faulty flush valve, refill valve, or overflow tube. Sometimes, damaged or cracked float balls and flappers are also responsible for this Overfilling.

In this article, we will discuss the mechanisms of the toilet reservoir working. Also, you will know more about the reasons and solutions for the overfilling of toilet reservoirs. Thus, if you are also facing this problem, this article will be helpful for you. Let’s go through the article.

why is my toilet tank overfilling

Working Mechanism Of Toilet Tank

Inside a toilet reservoir, a few components function in the toilet flush. Those components are:

  • Handle
  • Handle arm
  • Chain
  • Flapper
  • Flush valve
  • Fill valve
  • Refill valve
  • Float ball
  • Overflow tube
  • Drain opening

Flushing Mechanism

The handle is connected to the handle arm, which helps lift the chain. With the lifting of the chain, the flapper also moves from the flush valve. The flapper keeps the flush valve converted to prevent the flow of water into the toilet.

But, when the cover is removed with a raised handle chain, the flush valve becomes uncovered for the water. Consequently, the water runs through the valve and drain, opening into the waste of the toilet and flushing away the trash into the sewer line.

Refill Mechanism

This water rush will continue until the tank is empty. After that, the flapper will again fall back on the flush valve and cover it. As a result, the rush of water will stop from the tank. But, with the water level drop, the float ball will also come down.

Likewise, this floating ball is connected to the refill valve, which will be uncovered with the ball’s dropping. Then, water will start coming into the tank from the water line.

With the rising water level, the float ball will again come into its place and will cover the refill valve again. Now, the tank is again prepared for flushing.

Why Is My Toilet Tank Overfilling?

First, you need to know the reasons for this problem before fixing it. In this section, we will discuss a few common reasons for toilet tank Overfilling.

#1. Faulty Float Ball

If there is any problem with the float ball, it will be unable to float. Sometimes, there might be a problem with the float ball that the seal between them becomes loose. Even if it floats and covers the refill valve, due to the leak between seals, the water will keep coming.


  • Check if the float connects with a lever. If not, take the hanging lever and connect it to the refill valve.
  • Next, you need to connect the other end of the lever with the float ball.

#2. Clogged Float Ball

Due to some reasons, the float ball can become clogged with water. This happens when the ball becomes cracked, and the water enters inside it. As the weight becomes heavier for the water trapped inside it, it sinks inside the water.

Thus, no matter how much water comes inside the tank, the float ball will remain submerged. Hence, overfilling will occur.


  • Change the cracked float ball
  • You can also replace it with another rubber flapper

#3.The Damaged Fill Valve Seal

If there is a leak in the fill valve seal, water will keep entering continuously. If there is no issue with the overflow valve, the water will not leak outside but will always run.


  • Check for leaks or cracks in the fill valve seal
  • Repair or replace the damaged one

#4. Inappropriate Size Of The Overflow Tube

The wrong size of the overflow tube is also responsible for this problem. If you use a shorter length of the overflow tube, it will keep escaping water from the tank. On the other hand, if the overflow tube is shorter than the required size, it will cause the overflow of water from the tank.


  • Don’t try to fix this problem yourself
  • Call a professional plumber to fix this Problem

#5. High Level Of The Overflow Tube

The overflow tube functions to block the overflow of water from the reservoir. And the water level needs to be below the tube. But, if the overflow tube level becomes high for some unforeseen reason, the water will spill from the reservoir.


  • You have to set the level of this overflow tube to the appropriate level.
  • You can fix the level by cutting the overflow tube.
  • If you are not experienced enough, you shouldn’t try cutting the overflow tube yourself. Call a professional plumber for the job.

#6. Damaged Flapper

When the flapper becomes worn out, damaged, or cracked, it will not cover the flush valve adequately. Thus, the valve will be uncovered to the incoming water and keep flushing it through the drain line.


  • You have to check the flapper to see if it is damaged
  • You can repair the flapper if you want
  • If the flapper is unrepairable, you must replace it with a new one


In this FAQ section, we will try to answer a few most asked questions about Overfilling issues of toilet tanks.

Q: Which Are The Familiar Places For Toilet Tank Leakage?

The main culprit for leakage is cracked or damaged seals or valves. That’s why the most common places of damage are spud washers, bolt gaskets, and refill valves. Three of these are seals or valves and become damaged with time.

Q: What Should I Avoid Doing While Fixing An Overfilling Tank?

You shouldn’t remove any pipe that connects to the toilet or the water line. Otherwise, you may cause more severe issues, which will cost more to repair. That’s why always call a plumber if you think there are problems with lines.

Q: Why Should I Fix an Overfilling Tank?

If you don’t resolve the running tank issue, water utility costs will increase. Also, if you leave this problem untreated, it may cause the overflowing of your toilet. Then, it might take a lot of money to repair.


Slipping out water from the toilet tank is common even in this modern age. So, why is my toilet tank overfilling? There are multiple reasons behind this. But you have to know how the toilet flushing and refilling process functions to understand those reasons.

In most cases, you can resolve this problem yourself. However, there are also several critical repairs that you can’t fix by yourself. You might damage the components more if you are not experienced enough. That’s why we suggest you call a plumber to resolve those issues.

Related Read:

Is It Bad To Shut Off Water To Toilet?

Low Water In Toilet Bowl After Flushing – Common Issues And Fixes

How To Unclog A Toilet With A Plunger?