What a flapper does and when to replace it
The flapper is a rubber or plastic disc at the bottom of your toilet tank that lifts when you flush, letting water rush into the bowl. When it wears out, water leaks slowly from the tank into the bowl all day and night — you'll hear the tank refilling on its own, or notice your water bill climbing. A worn flapper is the most common reason a toilet runs constantly.
Flappers last three to five years on average, depending on water hardness and how often the toilet is used. Hard water and mineral buildup speed up wear. You don't need a plumber for this repair — the part costs $5 to $15, and the job takes less than half an hour once you have the right flapper model.
Key Takeaways
- Turn off the water supply at the shutoff valve under the tank before you start, then flush to empty the tank.
- The flapper is held in place by a clip or two small hooks on a rod that runs across the tank — you lift it straight up to remove it.
- Take the old flapper to the hardware store or look up your toilet model online to buy the exact replacement, because flapper sizes vary.
- The new flapper slides onto the rod the same way the old one came off, and the chain reconnects to the flush lever with a single clip.
Shut off the water and empty the tank
Look under the toilet tank on the left side. You'll see a small valve with a handle — this is the shutoff valve. Turn the handle clockwise until it stops. The water supply to the toilet is now off.
Flush the toilet once. The tank will empty and stay empty because the water is shut off. If water is still trickling in, the shutoff valve may be stuck or faulty — turn it as far as it will go, and if water keeps running, you may need to replace the valve itself, but that's a separate job. For now, proceed with the tank as empty as it will get.
Identify your flapper model before you buy
Lift the tank lid carefully — it's heavy and fragile. Set it on a towel on the floor where it won't tip. Look at the bottom center of the tank. You'll see a rubber or plastic disc sitting on top of a hole. That's the flapper. Attached to it is a chain that runs up to the flush lever on the side of the tank.
The flapper is held in place by a rod that runs left to right across the tank. The rod passes through two small holes or hooks on the flapper. To know which replacement to buy, you need either the toilet's brand and model number (usually stamped on the tank or bowl) or the flapper's size. Most flappers are either 2-inch or 3-inch diameter. Take a photo of the flapper and the tank's model number, or bring the old flapper itself to the hardware store. Staff can match it to the right replacement.
Remove the old flapper
Unhook the chain from the flush lever. The chain is clipped or hooked to a small arm on the lever — pull the clip straight out or unhook it by hand. The chain will now hang loose.
Lift the flapper straight up. It will slide off the rod. The rod stays in place. Set the old flapper aside. If the rod itself is bent or corroded, you may need to replace it too, but most of the time only the flapper wears out.
Install the new flapper
Slide the new flapper onto the rod, lining up the two holes on the flapper with the rod. It should sit flat on the hole at the bottom of the tank, just like the old one did. The flapper should move freely up and down on the rod — if it's too tight or too loose, you may have the wrong size.
Reconnect the chain to the flush lever. The chain should have a small clip or hook at the end. Attach it to the arm on the flush lever. The chain should be slightly slack when the flapper is resting — if it's too tight, the flapper will sit slightly open and water will leak. If it's too loose, the flapper won't lift all the way and the flush will be weak. Adjust the chain length by moving the clip up or down the chain, or by unhooking it and reattaching it one link higher or lower.
Test the flush and check for leaks
Turn the shutoff valve back on by turning the handle counterclockwise. Water will flow back into the tank. Listen for the tank to fill and the fill valve to shut off — this usually takes 30 seconds to a minute.
Flush the toilet. The flapper should lift smoothly, water should rush into the bowl, and the flapper should drop back down and seal. The tank should refill and then stop. If water keeps running into the bowl after the tank is full, the flapper is not sealing — the chain may be too tight, or you may have the wrong size flapper. If the flush is weak, the chain is probably too loose.
Wait 10 minutes and listen. You should not hear the tank refilling on its own. If you do, the flapper still isn't sealing. Check the chain tension again, or the flapper may be sitting crooked on the rod. If adjusting the chain doesn't fix it, the flapper size may be wrong — return it and try the other size.
Common problems and fixes
If the new flapper leaks right away, the most common cause is a chain that's too tight. The chain should have about half an inch of slack when the flapper is resting. Loosen it by one link and test again.
If the tank refills slowly but does eventually stop, the flapper may be sealing but the fill valve may be worn. That's a separate repair. If the tank refills quickly and never stops, the flapper is definitely not sealing — check that it's the right size for your toilet and that it's sitting flat on the hole.
If the flush lever feels stuck or hard to push, the chain may be tangled or caught. Make sure the chain hangs straight down and isn't twisted around the rod or other parts inside the tank.
Frequently Asked Questions
Do I need to turn off the water to replace a flapper?
Yes. Turning off the water at the shutoff valve lets you empty the tank so you can see and reach the flapper clearly. It also prevents water from splashing while you work. The shutoff valve is under the tank on the left side.
What if the flapper rod is bent or corroded?
If the rod is bent, the flapper won't seal properly no matter how new it is. You can buy a replacement rod kit at the hardware store — it includes the rod, the flapper, and the chain hardware. Installation is the same as replacing just the flapper.
Can I use any flapper or do I need the exact model?
Flappers come in different sizes, usually 2-inch or 3-inch diameter. Using the wrong size will cause leaks or a weak flush. Bring the old flapper or your toilet's model number to the store so staff can match the right one.
How do I know if the chain is the right length?
The chain should have about half an inch of slack when the flapper is resting at the bottom of the tank. If it's too tight, the flapper won't seal. If it's too loose, the flush will be weak. Adjust by moving the clip up or down the chain.
Why does my toilet still run after I replaced the flapper?
The most common cause is a chain that's too tight, pulling the flapper slightly open. Loosen it by one link. If that doesn't work, you may have the wrong flapper size, or the fill valve itself may be worn and need replacement.