How to Fix a Running Toilet: Diagnose and Deal With the Problem in 6 Steps

By Jennifer Beck Goldblatt

Toilets should be seen and not heard, which is why learning how to fix a running toilet is a skill most homeowners would be wise to pick up. (And you only thought that you just needed to know how to clean a toilet.) As one of the most common plumbing issues, a running toilet can also be one of the most costly—when left untreated. If you hear a toilet running, that means it's using water, and a constant flow of water can lead to sky-high water bills. A toilet that runs can go through hundreds of gallons of water in a day, equaling hundreds, maybe even thousands, of dollars over time. Most of the time, the root of the issue isn't so serious. More often than not, the flapper valve could need adjustment, or you may need to replace the toilet fill valve. Both are relatively small fixes that most homeowners can usually handle without calling in a professional plumber or having to remove the toilet and then having to install a new one.

"In most cases, DIY’ers should be able to tackle this issue on their own, but it's important the problem is solved quickly to avoid a drastically high water bill and a waste of resources," says Jim Reinhart, product leader and director at American Standard.

Here's how to stop flushing money down the toilet (literally) and get to the root of why your toilet won't stop running.

Having a basic understanding of the inner workings of a toilet will be helpful for anyone trying to diagnose problems with their own unit. Here's what's happening inside the tank:

When you press down on a toilet's flush lever, the rubber flapper (also called a flat valve) raises inside the toilet tank. This allows the water from the tank to empty into the bowl and push the waste down the toilet. As the water moves from the tank to the toilet bowl, the flapper slowly sinks down and rests on the flush valve. As the toilet flapper seals off the water to the bowl, the toilet fill valve (also called a ballcock) allows water to flow into the toilet tank, filling it up for the next flush.

"Unless the toilet has just been flushed, you should not be hearing any indication of running water," Reinhart says. "If you’re hearing these sounds, whether it be constant or every hour, it may be a sign of a bigger issue with your toilet." The cause of your noisy toilet? Either the float cup is positioned at the incorrect height, the chain on the toilet flapper has an issue, or the flapper seal or fill valve needs to be replaced. In rare cases, a running toilet may be due to a crack in the toilet tank, but this is something that you should be able to spot visually, since water will pool on the floor around the bowl or beneath the tank.

You won't need any special tools to figure out why your toilet is running, just your eyes, ears, and a set of hands. First, you’ll want to shut off the main water supply. There should be a shutoff valve or knob at the rear of your toilet, typically on the wall or floor. Turn the knob clockwise to shut it off. Next, remove the tank lid. Inside you’ll should see the main parts responsible for your toilet's water control: the flapper chain, flapper, overflow tube, a ball float or float cup, and fill valve.

Here are six reasons your toilet is running—from most to least common:

Fixing the chain is often the easiest solution.

The chain connected to the flapper at the base of the tank can cause issues if it is too long or too short. When it's too long, it can become caught in the flapper, preventing a tight seal. If this is the case, use your fingers to adjust the length of the flapper chain attached to the clip. If there are a lot of excess links, use pliers to trim the chain. Likewise, if the chain is too short or caught on something in the tank, it can cause water to flow constantly. Check to see if the chain is hooked onto anything (possibly even itself) and needs freeing. An old toilet may have a rusty flapper chain, which should be replaced altogether.

A flapper is like a water stopper.

Locate the flapper at the bottom of the tank and press it gently with your hand. You can also use a long screwdriver if you don't want to get your hands dirty. If doing so causes your toilet to stop running, then the flapper is faulty and needs to be replaced. Discoloration or any visual signs of ware or warping are also signs that you should replace the old flapper. If this is your issue, skip to below for next steps.

Too much water causes a waterfall effect in your toilet tank.

Ideally, the water level in the toilet tank should be 1 to 1.5 inches below the top of the overflow tube (also called an overflow pipe), an open-ended tube centrally located in the tank. When the water level is too high, water will constantly drain from the fill tube into the overflow tube, causing a running sound. To check this, you’ll need to turn the water supply to the toilet back on, by turning the knob that you previously closed in the opposite direction. If water continuously drains into that tube without stopping, you’ll want to lower the float to adjust the water level.

Think of the float ball as the commander of how much water is filled into the tank.

The float ball adjusts the water level. Use your fingers to gently bend the float arm connected to the often black, balloon-like float near the top of the tank to adjust its position and the float height. Flush the toilet and see if the running stops once the tank is filled.

A float cup sits on the fill valve. To adjust, look for a spring clip on its side and use your hand to press both sides in. You should now be able to raise or lower the float cup as needed. Once done, flush the toilet to determine if that fixed your issue.

Replacing the fill valve is typically less than $10.

If the above fixes don't work, you may need to replace your toilet's fill valve, typically located to the left of the overflow tube. It can become dirty or brittle over time, and may need replacing every few years. With the water supply off and the tank drained, unscrew the water supply line, located outside of the tank, by unscrewing the lock nut with a pair of pliers. You should then be able to pull the old fill valve up and out of the tank so you can bring it with you to the hardware store to make sure you purchase a new fill valve that is the same size. Once you have the replacement in hand, do the above steps in reverse to install, then adjust the float to your desired water level. Once done, flush the toilet to determine if that fixed your issue.

If you’ve determined that a faulty flapper is the cause behind your running toilet, replacing it should be an easy do-it-yourself fix. First you’ll want to remove the existing flapper. To do this, unhook the sides from the pins at the bottom of the overflow tube (that's the one in the center of the tank). Next, you’ll want to bring that flapper with you to a hardware store so you can buy one that is the same shape and dimensions as the one you’re replacing. "It is important to not mix and match the toilet parts as most toilets are configured to work optimally with parts from the same brand," Reinhart warns. To attach a new flapper, simply fit it into place and reattach the hooks and pins that you undid when removing the faulty flapper. Turn the water back on and see if that fixed the issue.

"Seal leakage is fairly common as toilets get older," admits Reinhart. It could be an issue that needs attention every three to five years. And remember, this can happen to each toilet in your house, so be sure to check the loo you may not use as frequently—like a guest bathroom—on a regular basis.

Several factors can contribute to the ware and damage of the components of your toilet tank, Reinhart says. Cleaning products, like tablets that go into the tank, often have aggressive chemicals like chlorine that can cause plastic parts to deteriorate over time. The flapper is especially susceptible to this type of damage. Likewise, those who rely on well water should stay up-to-date with maintenance to ensure that the water is treated correctly and won't cause any unnecessary damage.