How to Fix a Running Toilet: Checks and Repair Steps

Quick answer: Start by checking whether water is entering the overflow tube or leaking from the tank into the bowl. Those observations guide the next checks; they do not identify a replacement part by themselves.

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This guide covers common gravity-flush tank toilets. A canister, dual-flush or pressure-assisted toilet may need its own maker’s parts and procedure. Find the toilet’s tank/model number before ordering.

How the Tank Works

On a conventional flapper toilet, the handle lifts the flapper to release water into the bowl. The flapper then closes, and the fill valve refills the tank and stops at the set water level. Some toilets use a canister or another flush seal instead of a flapper. Compare the two jobs in our flapper versus fill valve guide.

A persistent leak can raise a metered water bill. Our Water Leak Cost Calculator estimates cost from the inputs you supply; it does not measure this toilet’s leak. For repair-price factors, see cost to fix a running toilet.

Step 1: Find the Leak Path Before Buying Parts

Lift the tank lid carefully and set it on a secure surface. Watch the water level and moving parts. The Toilet Diagnostic tool can help organize symptoms, but confirm the fault and model compatibility before buying its suggested part.

Water enters the overflow tube: compare the level with the toilet maker’s mark, check whether the float is obstructed, and follow the fill valve’s adjustment and maintenance instructions. On a Kohler, use the tank number with our Kohler fill valve guide.
The tank refills between uses: check the chain and handle, flush seal, valve seat and refill tube. A slow leak can have more than one cause.
Suspected tank-to-bowl leak: the EPA’s dye test (epa.gov) uses a few drops of food coloring or a dye tablet in the tank. Wait 10 minutes without flushing; color appearing in the bowl confirms a leak. Flush afterward to avoid staining. It does not prove that buying a flapper will fix every leak.

For a leak that persists, Fluidmaster’s water-level test (maker page: www.fluidmaster.com/toilet-problems/testing-toilet-tank-water-leak-toilet-bowl/) helps distinguish possible leak points: with a full tank, shut the supply off, do not flush, mark the level and check after 30 minutes. Repeat until the level stops falling. A result near the seal, overflow or tank bottom needs the corresponding inspection; use the maker’s full instructions rather than treating the result as an automatic purchase.

Replacement options after diagnosis and fit checks

Check the tank number and flush-system design first. A 2-inch or 3-inch label refers to the valve size, not a promise that every flapper with that label fits. Use our flapper size guide alongside the toilet and part makers’ instructions; canister and specialty seals need their own match.

Confirmed repair need	Option and limits
A conventional 2-inch flapper needs replacement (Step 2)	2-inch flapper: Korky 100BP. Korky says it fits most 2-inch flush valves, and it comes with a stainless steel chain.
A compatible 3-inch flapper needs replacement (Step 2)	3-inch flapper: Fluidmaster 5403. Fluidmaster says it fits most 3-inch flush valves. The listing says it is not designed for 2-inch valves.
Fill valve replacement is needed after adjustment and maker-directed maintenance (Step 3)	Fill valve: Fluidmaster 400H. Fluidmaster lists it for 2-inch and 3-inch flush valve toilets that use 1.28 to 3.5 gallons per flush, with height adjustable from 9 to 14 inches.
A compatible 2-inch flush valve needs replacement after the leak path is confirmed	2-inch flush valve kit: Fluidmaster K-507A-008. It includes a new flapper and a tank-to-bowl gasket. Fluidmaster’s instructions take the tank off the bowl to fit it, so it needs a two-piece toilet with a removable tank. Because of that step, we would not plan on it for a one-piece toilet. For a 3-inch valve, see our flush valve kits.

Korky 100BP: confirm your toilet’s fit, then check Amazon →

Fluidmaster 400H: confirm your toilet’s fit, then check Amazon →

Step 2: Inspect the Flapper or Flush Seal

Check for a caught chain, debris at the sealing surface or a damaged seal before replacing anything. A conventional flapper and a canister seal are different parts. Shut the supply off and drain the tank before removing a seal, following the toilet and replacement-part instructions.

Match the valve size, hinge arrangement and flush volume, then use the replacement’s adjustment instructions. The toilet flapper buying guide and Korky versus Fluidmaster comparison explain selection factors; neither guarantees a particular lifetime in your water conditions.

An American Standard Cadet, VorMax or Champion can use different seals. Match the tank number in our American Standard flapper guide, then confirm it with the maker’s parts information.

Step 3: Adjust, Maintain or Replace the Fill Valve

If the water level reaches the overflow, check the float’s movement and setting against the toilet’s fill line. If adjustment does not solve it, follow the valve maker’s cleaning or service procedure before deciding it needs replacement. Do not assume every running valve is worn out.

For a new valve, match tank clearance, refill arrangement and flush-system compatibility. Follow its height, critical-level, refill-clip and water-level instructions; do not push the refill tube down into the overflow. See the fill valve buying guide. For a Gerber toilet, use the model information with our Gerber parts guide; the brand alone does not prove fit.

Step 4: Check the Chain, Handle and Connections

The chain should let the flush seal close fully while allowing the handle to lift it. Use the seal maker’s slack and attachment instructions. Check whether the flush handle returns freely.

Inspect the water connector for leaks and damage. Replace it when its condition or maker’s instructions call for replacement, rather than buying one simply because the tank is open. Use the toilet supply line guide to match length and connections. Each connection has its own tightening instructions.

When a Flush Valve or Complete Kit Makes Sense

A damaged overflow tube or flush valve can require more work than a seal swap. A complete tank repair kit is an option when multiple compatible components actually need replacement; age alone is not a reason to replace them all. For a single flush-valve fault, compare flush valve kits.

The linked K-507A-008 is for suitable 2-inch flush-valve installations. Its instructions remove the tank from the bowl, so it requires a two-piece toilet with a removable tank. It is not a drop-in flapper repair, and that tank-removal step is why we do not suggest it for a one-piece toilet. Check tank bolt arrangement, gasket and clearance before ordering, and follow the exact kit manual when tightening its locknut and tank hardware.

When to Call a Plumber

Get help if you cannot identify the system or stop the water safely, the diagnosis remains unclear, parts are seized, a tank is cracked, or a repair leaks. You do not need to attempt tank removal or force a stiff shutoff valve. Water on the floor also needs prompt investigation.

For context on metered charges, see water leak costs in 31 U.S. cities. Use your own current rate and measured leak estimate rather than assuming this toilet matches an average.

Two Common Replacement Types—Only After Fit Checks

Korky 100BP 2-inch flapper — an option for a compatible 2-inch flush valve; check your size first.
Fluidmaster 400H PerforMAX fill valve — a fill valve option within the maker’s stated tank and flush-volume range.

Picking the right size and brand: the flapper guide and fill valve guide.

Water on the Floor? Check Separately

A floor leak needs a separate inspection. Dry the area and locate whether water comes from the connector, tank hardware, tank-to-bowl joint, condensation or the base. A puddle or sewer odor alone does not prove a failed wax ring.

If water is escaping, stop using the toilet and shut the supply off if you can safely. Do not use a blanket hand-tight-plus-quarter-turn rule on every connection. Follow the connector and toilet maker’s instructions; overtightening can damage parts or porcelain.

For a confirmed tank-to-bowl problem, match the tank-to-bowl gasket and hardware. If the leak or a rocking toilet involves the base, a plumber can check the seal, flange and surrounding structure. Get help for persistent leaks or water entering the floor.

Related Toilet Repair Guides

Frequently Asked Questions

How much does it cost to fix a running toilet?

The cost depends on the diagnosed fault, exact compatible parts, access and whether professional help is needed. A seal replacement and a tank-removal repair are different jobs; get a quote for the actual fault.

Why does my toilet run randomly every few minutes?

Intermittent refilling can mean tank water is leaking into the bowl. Check the chain, flush seal, valve seat and refill-tube placement before deciding which part, if any, needs replacement.

Can a running toilet raise my water bill?

Yes, a persistent leak can increase metered water use. The amount varies with the leak and local water and sewer charges; a symptom alone does not establish gallons or dollars lost.

Related: why your toilet is sweating.

If the toilet only runs in short bursts every few minutes rather than constantly, see the phantom flushing guide for intermittent tank-to-bowl leak checks.

If instead the tank refills too slowly after a flush, see why a toilet fills slowly.

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Compare compatible options: toilet flapper · fill valve · toilet repair kit.

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For broader water-use context, see our 2026 Home Water Waste & Cost Report.

Sources and Selection Notes

These options are compared from product specifications and instructions; this page does not claim hands-on testing. Fit guidance uses Korky 100/100BP (korky.com), Fluidmaster 5403 (maker page: www.fluidmaster.com/products/toilet/flapper/5403-universal-adjustable-3-flapper/), 400H (maker page: www.fluidmaster.com/shop/product/400h-performax-fill-valve/) and K-507A-008 (maker page: www.fluidmaster.com/products/toilet/flush-valves/k-507a-008-toilet-flush-valve-repair-kit/) maker information. Use the exact part’s current installation instructions and the toilet’s model information.