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How to fix a running toilet

A toilet that won't stop running is almost always one of three cheap parts inside the tank. Here's how to tell which one and fix it yourself.

Updated · 6 min read

  • DifficultyEasy
  • Time15–45 minutes
  • If you need helpPlumber

A toilet that keeps running, or that refills by itself every few minutes, is one of the most common problems in any home. The good news is that the fix is almost always inside the tank, and the parts are cheap. You don't need special skills or a plumber for most of it.

Water only does two things in a toilet tank: it comes in through the fill valve, and it goes out to the bowl through the flush valve, which is sealed by a rubber flapper. A running toilet means one of those two is not shutting off. Your job is to find out which one.

Plan on 15 minutes to find the cause. Replacing a flapper takes about 15 more. A new fill valve can take 30 to 45 minutes the first time.

What you'll need

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Before you buy parts, find your toilet's shutoff valve. It's usually on the wall or floor behind the bowl. Turn it clockwise to close it. If you can't find it or it won't budge, see how to find your water shutoff.

Find the cause in five minutes

Lift the lid off the tank and watch for a minute after the tank fills. You are looking for one simple thing: is water spilling into the tall open pipe in the middle of the tank? That pipe is the overflow tube.

  • Water is pouring into the overflow tube. The water level is set too high, or the fill valve isn't shutting off. Skip to adjust or replace the fill valve.
  • Water is not going into the overflow tube. Water is most likely slipping past the flapper into the bowl. Do the dye test below.
  1. Add color to the tank. Put a few drops of food coloring into the tank water. Don't flush.
  2. Wait 10 minutes. The EPA's WaterSense program says that if any color shows up in the bowl after about 10 minutes, you have a leak.
  3. Flush when you're done. Flush once to clear the dye so it doesn't stain the tank.

Color in the bowl means the flapper or its chain is the problem. Start with the chain, because it costs nothing to fix.

Check the flapper chain

The chain connects the flush handle's arm to the flapper. If it's too short, it holds the flapper slightly open. If it's too long, it can get caught under the flapper and keep it from sealing.

  1. Look at the chain with the tank full. It should hang with just a little slack. It should not be tight, and it should not be long enough to drape under the flapper.
  2. Adjust it. Unhook the clip and move it one or two links at a time. Flush and watch the flapper drop and seal.
  3. Trim extra chain. If there's a long tail, cut off the extra so it can't float into the way.

If the chain looks fine and the dye still shows up, the flapper itself is worn.

Replace the flapper

Flappers are rubber, and over time they warp, stiffen or collect mineral buildup. The EPA notes that a worn flapper is a common cause of toilet leaks and that replacing it is usually a quick fix.

  1. Shut off the water and flush. Close the shutoff valve behind the toilet, then hold the handle down to drain the tank. Sponge out what's left.
  2. Remove the old flapper. Unhook the chain from the handle arm. Slide the flapper's side ears off the pegs on the overflow tube, or slip the ring off over the top of the tube.
  3. Look at the seat. Wipe the round rim the flapper sits on with a soft cloth. If you feel grit or buildup, clean it gently. A cracked or pitted seat is a bigger job.
  4. Buy a match. Take the old flapper with you to the store, or check the model number inside the tank. Most are 2-inch or 3-inch.
  5. Install the new one. Attach it to the pegs or slide it over the tube, center it on the seat, and clip the chain with a little slack.
  6. Test it. Turn the water back on slowly, let the tank fill, flush a few times, and repeat the dye test.

Adjust or replace the fill valve

If water is running into the overflow tube, the fill valve is letting in too much. Fluidmaster, a major maker of toilet parts, says the water should sit within about 1 inch of the top of the overflow tube. Many tanks also have a water line marked on the inside wall.

  1. Lower the float. On a modern fill valve, the float is a cup that slides up and down the valve body. Turn the adjustment screw or clip on top to lower it. On an older toilet with a ball on a long arm, gently bend the arm down a little.
  2. Flush and check. Let the tank refill. The valve should shut off with the water below the top of the overflow tube.
  3. Clean the valve if it still runs. Shut off the water, remove the cap on top of the fill valve (check its instructions), and rinse out grit. Fluidmaster recommends cleaning first and replacing only if cleaning doesn't help.
  4. Replace it if needed. A fill valve kit comes with clear instructions and fits most toilets. You'll unscrew the supply line under the tank, remove the nut, swap the valve, and set the new height.

When to call a pro

Stop and call a plumber if:

  • Water is leaking onto the floor from under the tank or the base of the toilet.
  • The tank or bowl is cracked, even a hairline crack.
  • The shutoff valve won't close, or it drips when you turn it.
  • The flush valve seat itself is cracked or pitted, which usually means removing the tank.
  • You've replaced the flapper and fill valve and it still runs.

Renters: let your landlord know before you replace parts. Many leases cover plumbing repairs. Not sure which way to go? Try our fix it or call a pro quiz.

Keep it from happening again

  • Do the dye test a couple of times a year, even when you hear nothing.
  • Skip cleaning tablets that sit in the tank. Kohler warns that chlorine products can seriously damage the fittings inside the tank.
  • Listen for the tank refilling when nobody has flushed. That's the earliest sign of a flapper going bad.
  • Know where your shutoff is before you need it. Our toilet overflow guide shows what to do if the bowl starts to rise.

Common questions

Why does my toilet run for a few seconds every so often?

That short refill is called ghost flushing. Water is slowly leaking from the tank into the bowl, usually past a worn flapper, so the fill valve kicks on to top the tank back up. A dye test will confirm it.

Is a running toilet an emergency?

Usually not, but it wastes water and adds to your water bill every hour it runs. Turn off the valve behind the toilet if you can't fix it today, and turn it back on only to flush.

Can I use any flapper on my toilet?

Not always. Flappers come in different sizes, most often 2-inch and 3-inch, and some toilets need a brand-specific part. Take the old flapper to the store or look up your toilet's model number to get a match.

Do I need to turn off the main water to fix a running toilet?

No. Most toilets have their own shutoff valve on the wall or floor behind the bowl. Turn it clockwise until it stops. If it won't turn or it drips, use the main shutoff instead.

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