Why Your Toilet Keeps Running and How to Fix It

Start with a quick diagnosis

Before buying any parts, figure out where the water is going. Open the tank lid, flush the toilet, and watch what happens. If water continues to flow into the bowl after the tank has refilled, the leak is at the flapper or the flush valve seat. If water is spilling down the overflow tube in the center of the tank, the fill valve is not shutting off or the tank water level is set too high.

The EPA notes that household leaks can waste 180 gallons per week, and toilets are often the culprit. Most toilet leaks are due to old or worn-out flappers, which are inexpensive parts typically made from rubber, plastic, or silicone. Replacing one is quick and easy. Start with the flapper because it is both the most likely cause and the least expensive fix.

Flapper leaks: the most common cause

The flapper sits at the bottom of the tank and acts as a seal between the tank and the bowl. When you flush, the handle lifts the flapper, water drains into the bowl, and the flapper falls back into place. If the flapper does not seal completely, water continuously seeps into the bowl, and the fill valve keeps running to replace it.

Flappers wear out over time. Rubber can become soft, warped, or encrusted with mineral deposits that prevent a tight seal. Silicone flappers tend to last longer. Check for visible wear, and press down on the flapper by hand after a flush. If the running stops when you press on it, the flapper is the problem.

To confirm a flapper leak, add a few drops of food coloring to the tank water and wait 15 to 30 minutes without flushing. If colored water appears in the bowl, the flapper is leaking. This dye test is the standard diagnostic method recommended by plumbing professionals.

• Turn off the water supply valve behind the toilet before replacing the flapper.
• Remove the old flapper by unhooking the chain and sliding it off the flush valve ears.
• Install a new flapper that matches your flush valve size (2-inch or 3-inch).
• Attach the chain with a small amount of slack so the flapper closes fully.
• Turn the water back on and flush to test.

Fill valve issues: when the tank does not shut off

The fill valve controls the water entering the tank after a flush. It uses a float mechanism to shut off the water when the tank reaches the correct level. If the fill valve fails, it may keep running even when the tank is full, sending water down the overflow tube and creating the classic hissing or continuous running sound.

Fill valves can fail because of worn seals, mineral buildup, or a stuck float. A fill valve that is slow to shut off may also cause intermittent running. Before replacing the valve, try cleaning the inlet screen and adjusting the float. Many fill valves have a height adjustment screw or a float that can be moved up or down.

If cleaning and adjusting do not solve the problem, replace the fill valve. This is a straightforward job for a DIYer. Turn off the water supply, flush to empty the tank, disconnect the supply line, remove the old valve, and install a new one following the manufacturer's instructions. A universal fill valve fits most toilets, but check your toilet's specifications before buying.

For more detail on this repair, see our guide on replacing a toilet fill valve.

• Shut off the water supply valve behind the toilet.
• Flush the toilet to drain the tank, and sponge out remaining water.
• Disconnect the supply line from the fill valve.
• Unscrew the lock nut under the tank and lift out the old valve.
• Install the new fill valve, adjust its height, and reconnect the supply line.
• Turn the water on and check for a clean shut-off.

Tank level problems: water spilling down the overflow tube

The overflow tube is a safety mechanism. If the tank water level rises too high, excess water flows down the tube and into the bowl, which keeps the toilet running. The correct water level is usually about one inch below the top of the overflow tube, or at the marked water line inside the tank.

If the water level is set too high, adjust the float. On a float-arm fill valve, bend the arm downward slightly to lower the level. On a float-cup fill valve, turn the adjustment screw or slide the float clip down. After each adjustment, flush and check the level.

A misdirected refill tube can also cause running. The small tube that runs from the fill valve into the overflow tube should direct water down the tube, not spray it into the tank or allow it to siphon back. Make sure the refill tube is securely inserted into the overflow tube.

Other causes to rule out

If the flapper, fill valve, and tank level are all fine, check a few less common causes. A worn flush valve seat, where the flapper seals, can develop rough spots or mineral buildup that prevent a tight seal. A cracked overflow tube or a damaged tank gasket can also leak water continuously. These repairs are more involved but still doable.

A toilet that flushes on its own or runs intermittently may have a different problem, such as a handle that sticks or a chain that catches. See our guide on toilets that flush on their own for diagnosis. If your toilet is older or has other issues, it may be worth considering a replacement. High-efficiency models use 1.28 gallons per flush or less, which the EPA says can reduce toilet water use by 20 to 60 percent. See our best 1.28 GPF toilets guide.

Prevent future running toilets

Routine maintenance can prevent most running toilet issues. Inspect the flapper every six to twelve months for signs of wear. Clean mineral deposits from the tank and flush valve as needed. Periodically check the fill valve for leaks and ensure the water level is correctly set.

Replacing a worn flapper before it fails is one of the easiest ways to avoid wasted water. The EPA recommends fixing leaky flappers promptly because they are the most common source of toilet leaks. If you are buying a new toilet, consider models with certified performance. WaterSense labeled toilets are independently certified for both efficiency and performance, and many use 1.28 gallons per flush or less. Browse our best 1.2 to 1.4 GPF toilets and best WaterSense toilets for options.

What to check based on your symptom

Questions

Why does my toilet keep running after I flush?

The most common cause is a worn flapper that does not seal completely, allowing water to leak into the bowl. Other causes include a fill valve that fails to shut off, a tank water level set too high, or a damaged flush valve seat.

How do I know if my toilet flapper is leaking?

Add a few drops of food coloring to the tank water and wait 15 to 30 minutes without flushing. If colored water appears in the bowl, the flapper is leaking and should be replaced.

Can a running toilet waste a lot of water?

Yes. The EPA reports that household leaks can waste 180 gallons per week, and toilets are often the culprit. Fixing a running toilet promptly can save a significant amount of water.

Is it hard to replace a toilet flapper?

No. Replacing a flapper is a quick and easy DIY repair. Turn off the water supply, remove the old flapper, install a new one that matches your flush valve size, and adjust the chain for proper slack.

What should I do if my toilet still runs after replacing the flapper?

Check the fill valve and tank water level. If the water is spilling down the overflow tube, lower the float. If the fill valve does not shut off, clean or replace it. Also inspect the flush valve seat for mineral buildup or damage.

When should I replace my toilet instead of fixing the running issue?

If your toilet is old, has cracks, or has recurring leaks that are costly to repair, replacement may be the better choice. Modern high-efficiency toilets use 1.28 gallons per flush or less and can significantly reduce water use.