What You're Replacing and Why It Matters

A toilet flapper is the rubber seal at the bottom of the tank that lifts when you flush, letting water rush into the bowl. A fill valve (also called a ballcock) is the mechanism on the left side of the tank that refills the tank after the flush. When either one wears out, you get a constantly running toilet, weak flushes, or water that won't stop trickling into the bowl. Both parts are inexpensive—usually $15 to $40 each—and replacing them takes about 30 minutes with basic tools.

The good news: you do not need a plumber. These are the two most common toilet repairs a homeowner can do alone. The parts sit inside the tank where you can see and reach them, and the job requires only a wrench and a screwdriver.

Key Takeaways

  • Turn off the water supply at the shutoff valve behind or below the toilet before you start, then flush to empty the tank.
  • The flapper is a rubber disc at the tank bottom; the fill valve is a tall assembly on the left side—measure or photograph yours before buying replacements.
  • Flappers usually unclip from two ears on the overflow tube; fill valves are held by a large nut underneath the tank and require a wrench to remove.
  • After installation, turn the water back on and let the tank fill, then test the flush and listen for running water to confirm both parts work correctly.

Gather Your Tools and Identify Your Parts

Before you touch anything, turn off the water. Look behind the toilet at floor level or below the tank for a small valve with a handle. Turn it clockwise until it stops—this is your shutoff valve. Flush the toilet to empty the tank completely. If no shutoff valve exists, you will need to turn off the main water supply to the house.

Now look inside the tank. The flapper is a rubber or plastic disc sitting at the very bottom center of the tank, usually attached to a chain or rod that connects to the flush handle. The fill valve is a tall assembly (usually 4 to 6 inches high) on the left side of the tank, with a water inlet at the top and a large nut underneath where it passes through the tank bottom.

Take a photo of each part or note the brand name and model number printed on them. Bring that information to the hardware store or use it to order online. Universal flappers and fill valves exist, but matching your exact model ensures a perfect fit and eliminates guesswork.

Remove the Old Flapper

The flapper sits on two small ears or posts that stick up from the overflow tube (the hollow pipe in the center of the tank). Grip the flapper gently and lift it straight up—it should slide off those ears. If it is stuck, soak it with a spray bottle of white vinegar for a few minutes to soften mineral deposits, then try again.

Next, unhook the chain or rod from the flush handle lever. Most chains straightforward unclip; some are bolted on. If bolted, use a wrench to remove the bolt. Set the old flapper and chain aside.

Before installing the new flapper, rinse the two ears and the overflow tube with clean water and a cloth to remove any sediment or mineral buildup. A clean surface helps the new flapper seal properly.

Install the New Flapper

Slide the new flapper onto the two ears, making sure it sits flat and centered. The flapper should hang straight down without tilting. Reconnect the chain or rod to the flush handle lever, leaving just enough slack that the chain is taut when the handle is at rest but not pulling the flapper up. A chain that is too tight will cause the flapper to leak; one that is too loose will cause weak flushes.

A good rule: when the handle is released, the chain should have about a half-inch of slack. Adjust by moving the chain clip up or down on the lever arm, or by removing a link if the chain is too long. Turn the water back on and let the tank fill. Flush once and listen—if water continues to trickle into the bowl after 30 seconds, the flapper is not sealing. Check that it is sitting flat on the overflow tube and that the chain has the right amount of slack.

Remove the Old Fill Valve

The fill valve is held in place by a large nut (usually 1.25 inches wide) on the underside of the tank. You will need to reach under the tank, so you may need to lie on your back or use a mirror to see it. Place a bucket underneath to catch any remaining water.

Use an adjustable wrench to turn the nut counterclockwise. It may be tight, especially if it has not been disturbed in years. Once the nut is loose enough to turn by hand, unscrew it completely. The fill valve will now be free to lift out of the tank from the inside.

Before you remove it, note where the water inlet tube connects at the top—this is usually a small plastic or metal tube that brings water from the shutoff valve. You will reconnect the same tube to the new valve. Lift the old fill valve straight up and out of the tank.

Install the New Fill Valve

Check the new fill valve's height adjustment. Most fill valves have a clip or screw that lets you set the water level in the tank. Look for a mark on the valve that shows the correct height—it should be about one inch below the overflow tube. Adjust it now before installation to save time later.

Lower the new fill valve into the tank opening, guiding the inlet tube through the hole. From underneath, hand-tighten the large nut onto the valve threads, then use the wrench to snug it firmly—do not over-tighten, as this can crack the tank. The nut should be snug enough that the valve does not wiggle, but you should still be able to turn it by hand if needed.

Reconnect the water inlet tube to the top of the new fill valve. Most modern valves use a straightforward push-fit connection—push the tube straight onto the inlet until you hear a click. If your old tube does not fit, the new valve usually comes with an adapter.

Test Both Parts and Adjust

Turn the shutoff valve counterclockwise to restore water to the toilet. Listen as the tank fills—it should take 30 to 60 seconds. Once full, the fill valve should stop running water and the tank should be silent.

Flush the toilet. The bowl should empty completely and refill smoothly. Listen for any hissing or trickling after the tank is full. If water continues to run into the bowl, the flapper is not sealing—check the chain slack and the flapper position again. If the tank does not fill or fills very slowly, the fill valve inlet may be blocked; turn off the water, remove the inlet tube, and blow through it to clear any debris.

Let the toilet sit for five minutes, then check again. A small amount of water trickling into the overflow tube is normal and helps refill the bowl trap, but a steady stream means the flapper needs adjustment. If everything is quiet and the flush is strong, you are done.

Common Mistakes to Avoid

The most frequent error is leaving the chain too tight, which holds the flapper slightly open and causes constant leaking. Remember: slack is your friend. The second mistake is over-tightening the fill valve nut, which can crack the tank. Hand-tighten first, then use the wrench for just a quarter-turn more.

Do not forget to adjust the fill valve height before installation. If the water level ends up too high, water will spill into the overflow tube and waste water. If it is too low, the flush will be weak. Most valves have a straightforward clip adjustment—check the instructions that come with your new valve.

Finally, do not mix old and new parts. If the flapper is worn, the fill valve is probably worn too. Replacing only one often leaves you with a running toilet because the other part is still failing. Both are cheap; replace both at the same time.

Frequently Asked Questions

How do I know if my flapper or fill valve is the problem?

If water runs constantly into the bowl, the flapper is leaking. If the tank does not fill after a flush or fills very slowly, the fill valve is blocked or worn. If water hisses or trickles into the overflow tube (the hollow pipe in the center), the fill valve is not shutting off. You can also add food coloring to the tank—if it seeps into the bowl without flushing, the flapper is bad.

Can I replace just the flapper or just the fill valve?

Yes, but both parts wear at similar rates. If one is failing, the other is usually close behind. Replacing both at once costs only a few dollars more and saves you a second repair in a few months. If you are certain only one is bad, replacing it alone is fine.

What if the fill valve nut will not budge?

explore penetrating oil (like WD-40) and let it soak for 15 minutes. Try again with the wrench, turning slowly and steadily rather than jerking. If it still will not move, wrap a cloth around the nut for better grip. As a last resort, you can cut the water inlet tube and the overflow tube connection to remove the old valve without unscrewing the nut, then install the new one—but this is messier and takes longer.

Why is my new toilet still running after I replaced both parts?

Check the fill valve water level adjustment—it may be set too high, causing water to spill into the overflow tube. Lower it by one-quarter inch and test again. Also confirm the flapper chain has the right amount of slack. If the problem persists, the new flapper or fill valve may be defective; return it and try a replacement.

Do I need to turn off the main water supply if I cannot find the shutoff valve?

Yes. If there is no shutoff valve behind or below the toilet, locate your home's main water shutoff (usually in the basement, crawlspace, or outside near the meter) and turn it off there. After you finish the repair, turn it back on. Consider having a plumber install a shutoff valve at the toilet for future repairs.