How to Fix the Flapper on Your Toilet's Flush Valve

person removing the lid from a toilet tank

The Spruce / Michelle Becker

A Running Toilet Usually Has a Flapper Problem

Adjustable toilet flapper
Amazon

A simple toilet part known as the flapper is responsible for two of the most common problems with toilets. 

What Is a Flapper?

The flapper is a contraption in the toilet's tank that's responsible for draining water from the tank into the bowl when you flush. The flapper is attached to the tank by a chain; when you flush, it lifts the flapper, allowing water to pass.

Many toilets, especially newer style have a different design. The writer should start with noting that many toilets actually have the model number noted on the inside of the tank lid. It is always best to try & locate a parts breakdown. This is not always easy but there is obviously a benefit to this. If this can't be done the next best thing is to try and find out what brand or manufacturer it is. There is usually a stamp in the casting. Take some pictures of the toilet & the inside of the tank. This way you can walk into a plumbing supply & get some professional help in determining the correct parts needed to fix the toilet. Sometimes its more complicated than just a flapper or ballcock. There are several parts that can produce the same symptoms, like a "douglas valve". In addition the 1 piece toilet design uses more specialized parts.

Observe the Flapper to Diagnose the Problem

toilet tank flapper flush valve
Lavelle

Remove the cover from your toilet tank and look down at the large opening in the bottom of the tank. This is the flush valve, and in normal operation, there is a rubber or vinyl flapper designed to lift up away from the flush valve when the toilet handle is pressed to start the flush cycle. At the end of the cycle, the flapper is supposed to settle back down into the flush valve opening and seal it tightly until the next flush cycle is initiated. 

  • If the toilet doesn't flush completely unless you hold the handle down, it is usually because the flapper is not lifting fully away from the flush valve. 
  • If the toilet continues to run, this almost always occurs because this flapper does not fit properly into the flush valve opening. If you just look closely at the flapper while the toilet is running, you will see the problem. Because water is continuing to leak down through the flush valve into the toilet bowl, the water level in the tank never rises high enough to shut off the water flow. 

Once you determine which problem you have, look for the corresponding fix below. 

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Watch Now: How to Replace a Toilet Flapper

Note: Very old toilets may use a tank ball with lift rod rather than a flapper and lift chain to seal the flush valve opening. If this is your situation, consider replacing the flush valve unit with a more modern assembly. Modern kits offer a single piece that includes the flush valve, the refill tube, and flapper all in a single plastic unit.

If You Have to Hold the Lever Down Completely to Flush the Toilet

flush valve repair kit
Fluidmaster

One of the most common toilet problems is having to hold the flush lever down to flush the toilet. Fortunately, this is an easy fix.

The problem is caused by too much slack in the lifting chain that connects the flush lever to the flapper. When the chain has too much slack, it cannot lift the flapper high enough to allow the full amount of water to flow down through the flush valve; it closes prematurely, thereby stopping the flush.

To fix this problem, simply adjust the chain length so there is about 1/2 inch of slack. If the leftover chain hangs down too far and interferes with any part, trim the length of the leftover chain.

If the Toilet Continues to Run After It Flushes

Toilet
Erin Huffstetler

Sometimes water in the toilet tank will continue to flow even after the flush is completed. The problem is annoying, and it can be a tremendous waste of hundreds of gallons of water if it isn't fixed. 

This usually is caused by another issue with the flapper. When the flapper doesn't tightly reseal against the flush valve, water will continue to flow down into the toilet bowl. Because the water level in the tank never reaches the level necessary to shut off the water supply valve (ballcock), fresh water continues to enter the tank endlessly. 

There are several different fixes you can try here: 

  • Make sure the lift chain is not so long that it pinches between the flapper and the flush valve. If it is, water will leak down into the toilet bowl after the flush. Shorten the chain slightly so it doesn't get pinched beneath the flapper. 
  • Make sure the flapper is properly aligned so it seals correctly against the flush valve opening. You may be able to make small adjustments to the flapper that magically stop the leaking. 
  • If the rubber of the flapper is old and cracked, it will be unable to seal the flow of water into the tank. In this case, you'll need to replace the flapper. Or, you can replace the entire flush valve/flapper assembly with a convenient repair kit.