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

What’s Actually Wrong

A running toilet almost always comes down to one of four things: a worn flapper, a fill valve that won’t shut off, a chain that’s tangled or too tight, or a float set too high. The good news is most people can diagnose and fix it in under 20 minutes without calling a plumber.

How to Fix a Running Toilet: Quick Overview

If you’re looking up how to fix a running toilet before it wastes another gallon of water, the short version is: most fixes take under 20 minutes and cost less than $20 in parts. Start with the flapper and fill valve below, and if the toilet is old enough that repairs keep coming back, it may be worth running the numbers through our Repair or Replace Decision Tool. For other fast plumbing fixes, see our guide to unclogging a slow bathroom sink drain.

Tools You’ll Need

An adjustable wrench, pliers, a screwdriver, and a towel. If you already suspect the flapper or fill valve is bad, pick up a universal flapper or fill valve kit before you start so you’re not making two trips.

Step-by-Step Fix

Remove the tank lid and set it somewhere padded so it doesn’t chip. Look at the rubber flapper at the bottom of the tank. If it’s warped, cracked, or coated in mineral buildup, that’s usually your answer. Check the chain connecting the flapper to the flush lever. It should have a little slack, about a half inch, not be taut and not be so loose it tangles under the flapper. Look at the fill valve, the tall tube usually on the left side of the tank. If water is trickling into the overflow tube even after the tank fills, the fill valve or the float needs adjusting. Turn off the water supply valve behind the toilet before you replace or adjust any part. Adjust the float lower, or replace the flapper or fill valve if either is worn. Turn the water back on and flush to test. Watch a full refill cycle to confirm the running has stopped.

Watch the Repair

If you would rather see the parts before you open the tank, this short walkthrough from Ask This Old House covers the same flapper and fill-valve repair described above.

When to Call a Plumber

If you’ve replaced the flapper and fill valve and the toilet still runs, or if you notice water pooling around the base, the problem is likely further down, such as a cracked tank or a bad wax ring, and it’s worth bringing in a licensed plumber before it causes water damage.

A running toilet can waste hundreds of gallons a day, so it’s worth fixing quickly even if you end up calling in a pro. This guide is for general reference; if you’re not comfortable working with your toilet’s water supply, a plumber can usually handle this repair in well under an hour.