Why Does Toilet Run After Replacing Flapper

Toilet run after replacing flapper is the most common concern. But why does your toilet keeps running after changing the flapper? As the toilet flapper is new. Obviously, it should work more accurately. Right?

Don’t get me wrong here. Your analysis may be incorrect in this case. For whatever reason, just the new flapper may not work always.

Maybe worse instead of better as in your case – toilet flapper leaking after replacement.

In order to install a new flapper, you have to pay attention to some parameters like exact size, weight according to the toilet model, etc. 

There is four possible cause for a toilet still running after replacing seal- Wrong size Flapper, The wax seal does not seal, The chain adjustment, The water tanks fill valve is set too high

There are many more things to watch before buying a flapper that you can know by reading this post.

Today you get your answer why does your toilet run after replacing the flapper, and how do you stop the toilet flapper from running.

Before know why does your toilet still running after changing the flapper? I want you to know the flapper mechanism and necessary parameters.

What is a Toilet Flapper & How it works?

Toilet Flapper present between the toilet tank and bowl, it is made with either plastic or rubber material. A flapper AKA flush seal deals with the water pressure. It is responsible for 

i.holding water in the tank, 

ii. Whenever press the lever or handle it open and allow the water to go down the bowl, 

iii. prevent leaking or running toilets.

How does a toilet flapper work?

Step1- Press the lever or handle

Step2– A chain connected to the flapper lift the upward side

Step3– When the flapper lifts up, the seal is open to allow runs through the bowl and wash out all waste

Step4– The flapper open until the flush is complete

Step5– After the full flush- the flapper drops down its seat and again seal the water so the water can’t run without any reason.

Step6– This is a cyclic process

A flapper is an inexpensive yet valuable part of the flush mechanism. It can prevent running water also cause running water.

Problems with flappers occur every 2 to 3 years because they withstand water pressure, if there is hard water, the lime is destroyed very quickly after the build-up, the seal of the flapper becomes thin.

It is very easy to change the flapper, but if you do not buy the right flapper, you will face problems like this. 

Why does the toilet run after replacing the flapper? 

It is very easy to change the flapper, but if you do not buy the right flapper, you will face problems like this. 

Toilet flappers are available in varied sizes, shapes, and ingredients. Your best option for a home toilet is a normal rubber flapper, which allows just a little bit of flexibility to produce a strong seal.

There is four possible cause for a toilet still running after replacing seal- i. Wrong size Flapper, ii. The wax seal does not seal, iii. The chain adjustment, iv. The water tanks fill valve is set too high

The most probable cause for a running toilet after changing a flapper is THE WRONG SIZE FLAPPER

Whenever you bring a new flapper, it may not be fit because all the flapper called universal that fit into any seal does not mean right for you.

If you have a 3-inch trapway, then you need a 3-inch in another hand. If you need two inches, then 3 inches do not fit perfectly into the seal.

A wrong size flapper is responsible for continuous flowing water, although it’s new. The size matter here.

How to choose the right toilet flapper?

There are three varieties of a flapper, Aka flush seal- tank ball, rubber, and seat disk.

The Tank Ball-type sits on top of the overflow pipe. When the toilet is flushed, the chain lifts the rubber ball and releases the water to pass through.

The tank ball flapper’s ball must be in the correct position of the chain. Otherwise, it can not create a proper seal, and the toilet is running.


Rubber is most visible and usually present in new toilets.

The rubber seal flapper fastens a cup to the overflow pipe. It is a typical mechanism of your bathroom.

If the chain adjustment is not correct,- you have to deal with the flush problem.

Seat Disk is typically seen in the oldest model. It has a small disk-like plate that mainly shields the overflow pipe and stops leakage.

To determine the right size flapper look at the flush flap duct opening. It is the present bottom of the toilet tank where the water permit to go down.

The drain opening size is around an orange or baseball- the flapper size must be 2 inches. 

On the other hand, the opening valve seems grapefruit size, then 3 inches is perfect for you.

Smaller or larger sizes never create the seal, and for that reason, either the flapper is new, it can’t hold the water.

Read More- How to fix a slow filling toilet

The Toilet Still Running After Water Turned Off 

Maybe your toilet is still running after water is turned off. Right? – This is because of either the poor chain adjustment or the wax seat not adhere.

After changing with a perfect size flapper sometimes trouble with running water again. 

After installing the flapper we need to adjust the chain too. If the chain is short, then the flapper won’t close, and the toilet is running.

The wax seal (seat) is the present bottom of the tank just top of the flush valve opening.

The flush seat attaches with adhesive to protect from any leakage.

The adhesive should rest for 3o to 45 minutes to be more cloggy. In case the glue does not stick that much, the toilet keeps running.

The water tank’s fill valve is set too high causing a leaking toilet.

Another reason for a rushing toilet is – the refill tube is constantly drawing water into the pan. This usually occurs whenever the fill tube is excessively high and not correctly placed in the overflow pipe.

Once the toilet’s tank fill valve is set too high, water will insert the overflow tube and make the toilet overflow.

Check the level of water is never more than a quarter-inch above the tip of the outlet pipe. Lowering the ballcock can fix the issue.

Now you may question yourself how do I stop my new flapper from leaking.

How do you stop a toilet flapper from running? 

To stop a toilet flapper from flowing follow these steps-

Step1- Get the right size with the right shape flapper first.

Step2– If your flapper is perfect for sealing, make sure to check the chain length. The chain which one end attached with the handle lever and another end with the flapper. 

Step3- Before place, the new flapper, clean the entire area with cloths, rub the minerals clog. Secure the flush valve seal. Wait for 30 to 45 minutes.

Step4– Check after the tank is full.

Can a bad flapper cause a toilet to run?

Yes. The flapper is so subtle and important for flushing time. The flapper can prevent water from leaking and also increase the water pressure same time.

Flapper has mostly worn out every two or three years later. It is inexpensive and made from rubber or plastic.

A bad flapper always responsible for a running toilet also can cause low flush water in the bowl.

Read more- Toilet bowl not filling with water but the tank is full

Final word for a toilet run after replacing a flapper

The most typical issue is toilet run after replacing the flapper. But why does your toilet continue to run after you replace the flapper?

Because the toilet flapper is brand new. Obviously, it should function more precisely. Right?

Don’t misunderstand me. In this instance, your analysis might be wrong. For whatever reason, the new flapper may not always work.

As in your instance, the toilet flapper leaking after repair, things may have gotten worse rather than better.

To install a new flapper, you must pay attention to certain characteristics such as correct size, weight based on the toilet model, and so on.

There are many more things to consider before purchasing a flapper that you can learn about by reading this page.

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