How to Replace a Toilet Flapper

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Anatomy of a Toilet

anatomy of a toilet illustration
Illustration: The Spruce / Bailey Mariner

 A standard gravity-flush toilet is remarkably simple in design, but having a good understanding of its mechanism will help you understand what can go wrong. It many cases, you'll be able to fix problems without incurring the expense of a professional plumber. 

A gravity-flush toilet consists of the following parts:

  • Fill valve: Also known as the ballcock or water supply valve, the fill valve is what delivers fresh cold water into the tank. The fill valve has a built-in float device that controls the water flow—opening when the water level in the tank drops, closing when the water level is once again near the top of the tank. 
  • Toilet tank: This serves as a reservoir for the water that will be released downward when a flush cycle is initiated. 
  • Flush valve: This is the opening in the bottom of the tank that connects to the toilet bowl. The flush itself occurs when water stored in the tank is released downward through the flush valve. The flush valve unit is integrated with the overflow tube and provides a mounting point for the flapper. 
  • Flapper: This is a rubber seal that closes off the flush valve to keep water in the tank, and which opens up when the handle lever is pressed. Lifting the flapper initiates the flush cycle, allowing water to rush down into the toilet bowl. When the flapper drops back into place as the flush concludes, the tank can begin to refill with water. 
  • Handle and lever:  This is a manually operated lever connected to a lift chain that lifts the flapper away from the flush valve when the toilet is flushed. 
  • Overflow tube: As part of the flush valve unit, the overflow tube serves two functions. First, it provides an escape route for excess water to drain down into the bowl should the fill valve fail to shut off as it's supposed to. Second, it allows a small stream of water delivered by a refill tube from the fill valve to flow down into the toilet tank. This small stream of water refills the standing water level in the toilet bowl. 
  • Toilet bowl and trap: The toilet bowl is integrated with a loop-shaped trap built into the body of the toilet. Together, this configuration holds standing water that seals off the sewer system from the bathroom. During the flush cycle, water and waste material in the bowl pushes through the trap and into the drain pipes. 

Diagnosing a Flapper Problem

Replacement toilet flapper
Aaron Stickley

When a toilet continues to run after you flush it, there are several possible causes, but a good place to start is by simple observation. If you take the cover off the tank of your toilet and peer inside, you will see an unusual component down in the bottom: a kind of hinged flap valve made of plastic and soft rubber (usually black or red) that is connected to the chain hanging down from the flush handle lever. This component is known as the flapper.

If you then flush the toilet, you'll see that the chain lifts up the flapper, allowing the water to rush down into the toilet bowl. This initiates the flush cycle. As the water empties from the tank, the flapper drops back down like a trap door, closing the valve so the tank can refill for the next flush. 

When a toilet continues to run after a flush cycle, it's usually because the flapper fails to seat itself properly back over the flush valve opening. This allows water to trickle down into the toilet bowl. If the tank level remains low enough, the fill valve will remain open as it continues its attempt to refill the tank. While sometimes there are adjustments you can make to the flapper, in other instances the problem occurs because the rubber of the flapper hardens over time and can no longer seal the valve. The solution? Replace the flapper with a matching new part.

Tools and Supplies You Will Need

  • Replacement flapper with lift chain

Turn Off the Water

Turning off the water to the toilet
Aaron Stickley

Turn off the water to the toilet by closing the shutoff valve located on the water supply line leading to the toilet; turn the handle on the valve clockwise until it stops. Drain the toilet tank by flushing the toilet. If necessary, hold the flush handle down until most the water is out of the tank. 

Remove the Old Flapper

Removing old toilet flapper
Aaron Stickley

Disconnect the flapper chain from the flush handle lever. This lever is a horizontal bar that runs from the flush handle to a position just above the flapper. There is usually a small clip on the top end of the chain that hooks into one of the holes on the handle lever. Undo the clip and let the chain drop; you will replace this chain as you install the new flapper.  

Slip the side ears of the flapper off of the pegs extending from the sides of the flush valve tube. On flappers made of hard plastic, these ears will snap loose; on flappers made of soft rubber, the ears simply slide off the pegs.

Prepare the New Flapper

New toilet flapper with ring cut off
Aaron Stickley

How you set up the flapper will vary depending on your toilet's design:

  • The most common toilet configuration has the flapper attached to pegs on the sides of the flush valve tube. In this case, cut off the ring (if there is one) on the back of the new flapper—it won't be needed.
  • If your flush valve doesn’t have the side pegs for the flapper, use the ring provided with the new flapper to slide the flapper into place over the overflow tube.

Install the New Flapper

New toilet flapper
Aaron Stickley
  1. Put the new flapper into place and hook each ear of the flapper onto one of the pegs on the sides of the flush valve.
  2. Connect the flapper chain onto the handle lever, adjusting the chain length as needed. When the handle lever is in the resting position, the chain should be relaxed, with a little bit of slack. If the chain is too tight, the flapper may not close completely. If the chain has too much slack, it can get caught under the flapper and prevent it from fully seating in the flush valve opening.
  3. Turn the water back on by turning the shutoff valve counterclockwise all the way.
  4. Test the new flapper and the chain length by flushing a couple of times and watching the flapper go up and down.