What you are replacing and why it matters

The fill valve, flush valve, and flapper are the three parts that control water flow in your toilet tank. The fill valve refills the tank after you flush. The flush valve opens to let water into the bowl. The flapper is the rubber seal that sits on top of the flush valve and lifts when you press the handle. When any of these wears out, you get a running toilet, a weak flush, or water that leaks into the bowl all day.

Replacing these parts costs between $15 and $40 in hardware, takes 20 to 45 minutes, and requires no special tools beyond a wrench and a screwdriver. The parts are standard across most toilets made in the last 20 years. Older toilets or unusual models may need a trip to the hardware store to match your tank size, but the job itself is the same.

Key Takeaways

  • Turn off the water supply at the shutoff valve under the tank before you start, then flush to empty the tank.
  • The fill valve unscrews from underneath the tank with a wrench; the flush valve comes out from the bottom and requires a large wrench or adjustable wrench.
  • The flapper is a rubber disc that sits on top of the flush valve and lifts off by hand once you remove the chain or strap holding it.
  • New parts come with instructions and usually fit into the same holes as the old ones, so you can install them in reverse order.
  • After installation, turn the water back on and let the tank fill, then test the flush and listen for leaks or running water.

Turn off the water and empty the tank

Locate the shutoff valve on the water line under the toilet tank, on the left side where the line enters. Turn the handle clockwise until it stops. If the handle is a small oval knob, turn it a quarter turn. If it is a lever, turn it 90 degrees so it points down or perpendicular to the pipe.

Flush the toilet once. The tank will empty and the fill valve will stop trying to refill because the water is shut off. If water continues to trickle in, the shutoff valve is not fully closed; turn it again until it stops completely. Leave the tank empty for the next steps.

Remove the old fill valve

The fill valve is the tall assembly in the left side of the tank. Look underneath the tank from below. You will see a large nut holding the valve to the bottom of the tank. Place a wrench on that nut and turn it counterclockwise. Use your other hand to hold the valve steady from inside the tank so it does not spin.

Once the nut is loose, unscrew it by hand until it comes off completely. The valve will drop out of the tank. Disconnect the water supply line from the bottom of the valve by turning the compression nut counterclockwise with a wrench. Set the old valve aside.

Remove the old flush valve and flapper

The flush valve is the large opening at the bottom center of the tank. Look underneath the tank. You will see a large nut holding the flush valve in place. This nut is usually wider than the fill valve nut and may require a large adjustable wrench or a specialized flush valve wrench. Turn the nut counterclockwise while holding the valve steady from inside the tank.

Once the nut is loose, unscrew it by hand and remove it. The flush valve will come out from the bottom. Inside the tank, you will see the flapper — a rubber disc sitting on top of where the valve was. Lift the chain or strap attached to the flapper and unhook it from the flush handle lever. Then lift the flapper straight up and off the post it sits on. Discard both the old flush valve and the old flapper.

Install the new flush valve and flapper

Take the new flush valve and insert it into the hole from the bottom of the tank, pushing it up until the threaded part sticks out below. From underneath, thread the large nut back on by hand first, then tighten it with your wrench. Do not over-tighten; snug is enough. Reconnect the water supply line to the fill valve connection on the flush valve if your new valve has one.

Place the new flapper on top of the flush valve post. It will sit flat and rest on the rubber seal. Attach the chain or strap to the flush handle lever. The chain should have a small amount of slack — about half an inch — when the handle is at rest. If the chain is too tight, the flapper will not seal properly and water will run. If it is too loose, the flush will be weak. Adjust by moving the chain attachment point on the lever or by removing a link if the chain is too long.

Install the new fill valve

Take the new fill valve and insert it into the hole on the left side of the tank from the inside. The threaded part will stick out underneath. From below, thread the large nut back on by hand, then tighten it with your wrench until snug. Do not over-tighten.

Reconnect the water supply line to the bottom of the fill valve by threading the compression nut clockwise with your wrench. Hand-tighten first, then use the wrench for a final quarter turn. The line should not leak when water pressure is on.

Test the new parts and check for leaks

Turn the shutoff valve counterclockwise to turn the water back on. The fill valve will begin to refill the tank. Listen for any hissing or spraying from underneath — a sign the water line is not seated properly. If you hear spraying, turn the water off, tighten the compression nut another quarter turn, and turn the water back on.

Let the tank fill completely. Once it stops, press the handle and flush. The tank should empty and refill normally. The flush should be strong and the water should stop running after about 30 seconds. If water continues to run into the bowl after the tank is full, the flapper is not sealing; check that the chain has the right amount of slack and that the flapper is sitting flat on the valve. If the tank does not fill or fills very slowly, the fill valve may be installed backward or the water line may be kinked.

Frequently Asked Questions

What if the old parts are stuck and will not unscrew?

Mineral buildup from hard water can freeze nuts in place. Spray the nut with penetrating oil and wait 15 minutes, then try again. If it still will not move, wrap a rag around the nut for better grip and use a larger wrench for more leverage. Do not force it hard enough to crack the porcelain.

How do I know which fill valve or flush valve to buy?

Take a photo of the old parts or bring them to the hardware store. Most modern toilets use standard 2-inch flush valves and universal fill valves that fit any tank. The staff can match your old parts or recommend a universal replacement that works with your tank size.

Can I replace just the flapper without replacing the flush valve?

Yes. The flapper is the easiest part to replace and often fixes a running toilet on its own. Unhook the chain, lift the old flapper off, and set the new one in place. This takes five minutes and costs $3 to $8. If the toilet still runs after a new flapper, the flush valve seat is worn and you will need to replace the valve itself.

What if water leaks from underneath the tank after I install the new valve?

The compression nut on the water supply line is not tight enough. Turn off the water, use a wrench to tighten the nut another quarter turn, and turn the water back on. If it still leaks, turn off the water again and check that the rubber washer inside the nut is seated properly and not cracked.

Do I need to turn off the water if I am only replacing the flapper?

No. The flapper sits on top of the flush valve and does not touch the water supply. You can replace it with the water on. However, turning the water off first makes the job cleaner and safer if you accidentally bump something.