Job guides / Bath / Plumbing / Fix a Running Toilet
The Job Guide

Fix a running toilet in under an hour.

The short answerA running toilet is almost always one of two parts. If water trickles into the overflow tube, lower the float or replace the fill valve. If the tank refills on its own now and then, the flapper is leaking: replace it and set the chain with a little slack. Shut off the supply valve first. Most fixes take 15–60 minutes and cost $6–$20 in parts.

A running toilet can waste a lot of water, and the fix is usually a $6 part. Here's how to tell which part is failing and what to swap in.

DifficultyEasy
Time15–60 minno special tools
DIY cost$6–$20estimate
Hiring a proVaries by areaestimate

DIY range is the Home Depot price of the parts below as of Oct 14, 2026. We didn't find a reliable published pro rate, so none is shown.

Fix a Running Toilet
6 stepsEvery pick rated about 4.5★ or higher, from hundreds to thousands of reviews.
Photo: Peter Muniz on Unsplash
Your Match

The kit, vetted.

Tick items off as you shop. Ratings and review counts were checked on 2026-10-14. Home Depot prices are as of 2026-10-14. Amazon shows its price at checkout.

Tools

1 items
QEP Extra Large Sponge, 3-Pack
Best ValueSponge

QEP Extra Large Sponge, 3-Pack

Soak up the last water in the tank before you swap the fill valve.

Home Depot 4.6 (2,443)$4.44View →
Affiliate link placeholder · Home Depot prices as of 2026-10-14 · Amazon prices shown at checkout

Materials

4 items
Fluidmaster PerforMAX Fill Valve + 2" Flapper Repair Kit
Top PickRepair kit

Fluidmaster PerforMAX Fill Valve + 2" Flapper Repair Kit

Replaces both usual culprits at once. Best if the toilet is 10+ years old.

Home Depot 4.5 (4,384)$17.48View →
Affiliate link placeholder · Home Depot prices as of 2026-10-14 · Amazon prices shown at checkout
Fluidmaster PerforMAX Universal Fill Valve (400H)
Top PickFill valve

Fluidmaster PerforMAX Universal Fill Valve (400H)

For water running into the overflow tube. Adjusts to fit most tanks.

Home Depot 4.6 (7,137)$14.98View →
Affiliate link placeholder · Home Depot prices as of 2026-10-14 · Amazon prices shown at checkout
Fluidmaster PerforMAX 2" Universal Flapper (502P21)
Best ValueFlapper

Fluidmaster PerforMAX 2" Universal Flapper (502P21)

For a toilet that refills on its own (a "phantom flush"). Fits most 2" flush valves.

Home Depot 4.6 (3,309)$6.48View →
Affiliate link placeholder · Home Depot prices as of 2026-10-14 · Amazon prices shown at checkout
Korky 3" Premium Toilet Flapper (3060CM)
3" valvesFlapper

Korky 3" Premium Toilet Flapper (3060CM)

For newer toilets with a 3" flush valve. Measure the opening first.

Home Depot 4.5 (3,016)$11.98View →
Affiliate link placeholder · Home Depot prices as of 2026-10-14 · Amazon prices shown at checkout
The Method

Step by step, start to finish.

  1. 01

    Find the leak

    Lift the lid. Water spilling into the overflow tube points to the fill valve. Intermittent refills point to the flapper. Food coloring in the tank that shows up in the bowl confirms a flapper leak.

  2. 02

    Shut off & drain

    Close the supply valve behind the toilet, flush, and sponge out what's left in the tank.

  3. 03

    Adjust the float first

    Set the water level 1/2"–1" below the top of the overflow tube. Many runs stop right here.

  4. 04

    Replace the flapper

    Unhook the old flapper from its pegs and the chain, clean the valve seat, and fit the new one. Leave about 1/2" of slack in the chain.

  5. 05

    Replace the fill valve

    Disconnect the supply line, unscrew the lock nut under the tank, drop in the new valve at the right height, and clip the refill tube to the overflow.

  6. 06

    Refill & test

    Open the supply, let the tank fill, check for drips under the tank, and flush a few times.

Watch First

See it done, then do it.

Our picks of the clearest tutorials. Credit and copyright belong to the creators.

This Old House

How to Repair Toilet Tank Components | Ask This Old House

Richard Trethewey on flappers, fill valves and tank parts.

Visit channel ↗
The Home Depot

How to Fix a Leaky Toilet | How to Stop a Running Toilet Tank

A quick diagnosis, then fill-valve and flapper swaps.

Visit channel ↗
Prefer to read?
How To Fix a Running Toilet, from This Old House
Read the guide ↗
Good Questions

Before you start.

How do I know if it's the flapper or the fill valve?

Water flowing into the overflow tube means the fill valve or float. A tank that refills by itself every so often means a leaking flapper.

2-inch or 3-inch flapper?

Measure the flush-valve opening at the bottom of the tank. Most older toilets are 2" and many newer ones are 3".

Do I need a plumber?

Usually not. Call one if the shutoff valve won't close or leaks, or if the tank or bowl is cracked.

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