How to Stop a Running Toilet (Step-by-Step)

Quick answer

A running toilet is usually fixed by replacing a worn flapper or adjusting/replacing the fill valve. Turn off the water supply, inspect the flapper seal and chain slack, then replace inexpensive tank parts if needed. Most repairs take under 45 minutes and cost less than $25.

A toilet that won't stop running wastes water and money—but the fix is often straightforward. Before you call a plumber, inspect the two most common culprits inside the tank: the flapper (the rubber seal at the bottom) and the fill valve (which refills the tank after each flush).

What causes a toilet to keep running?

When you flush, the flapper lifts and water rushes from the tank into the bowl. The flapper should drop and seal once the tank empties. The fill valve then refills the tank until the float shuts it off.

Running continues when:

For deeper diagnosis, see our guide on why a toilet keeps running.

Tools needed

• Adjustable wrench or pliers
• Bucket or towels
• Flashlight
• Replacement flapper (match your toilet model if possible)
• Optional: universal fill valve kit

Materials needed

• Replacement flapper ($3–$8)
• Optional fill valve kit ($10–$20)
• Clean rag

Step-by-step: fix a running toilet

1. Turn off the water and flush — Rotate the shutoff valve behind the toilet clockwise until it stops. Flush once to empty most of the tank. Sponge remaining water into a bucket so you can work dry.

2. Inspect the flapper and chain — Check whether the flapper sits flat on the flush valve opening. The chain should have about 1/2 inch of slack—too tight prevents sealing; too loose can hang up on other parts. Clean mineral buildup with a rag.

3. Replace the flapper if worn — Unhook the old flapper from the overflow tube ears and chain. Install the new flapper the same way. Many flappers are universal; for odd sizes, bring the old part to a hardware store. For a dedicated walkthrough, see how to replace a toilet flapper.

4. Check the water level and float — Turn the water back on. The water level should sit about 1 inch below the top of the overflow tube. If water flows into the tube, lower the float or adjust the fill valve per manufacturer instructions—see how to adjust toilet water level.

5. Replace the fill valve if needed — If the valve won't shut off or is noisy and old, install a universal fill valve following the kit directions—typically removing the old unit, adjusting height, and securing the lock nut underneath the tank. See our fill valve replacement guide for full steps.

6. Test and monitor — Flush several times. Listen for running water 10–15 minutes later. Add a few drops of food coloring to the tank; if color appears in the bowl without flushing, the flapper still isn't sealing.

Common mistakes

• Buying a flapper without checking shape/size (some toilets need specific models)
• Leaving the chain too tight, which lifts the flapper slightly
• Setting the float too high, sending water down the overflow tube
• Overtightening the fill valve lock nut and cracking the tank

Troubleshooting after repair

Prevention

• Follow our toilet maintenance checklist for monthly and seasonal checks
• Replace flappers when stiff or when dye tests fail—not on a rigid calendar alone
• Avoid drop-in tank tablets that can corrode rubber parts
• Periodically check the shutoff valve turns freely

When DIY is appropriate

Replacing tank internals is appropriate for most homeowners comfortable turning off water and working inside the tank. This is not the same as clearing main line clogs or replacing a wax ring seal at the floor flange—those may require professional plumbing help.