How to Fix a Running Toilet: Flapper, Fill Valve, and Float Repair Guide

Frequently Asked Questions

How do I know if my toilet flapper is bad?

Put a few drops of food coloring in the tank. Wait 10 minutes without flushing. If color appears in the bowl, the flapper is leaking. A worn flapper feels slimy or stiff to the touch and often has visible mineral buildup around the edges where it seals against the flush valve seat.

Why does my toilet run for a few seconds, stop, then run again?

This is called phantom flushing or ghost flushing. It means water is slowly leaking past a faulty flapper into the bowl until the tank drops low enough to trigger the fill valve. The tank refills, then the cycle repeats. Replace the flapper — it's almost always the cause. If a new flapper doesn't fix it, the flush valve seat may be pitted and need replacement.

How do I adjust the float on my toilet?

For a ball float: bend the float arm downward slightly or turn the adjustment screw at the valve to lower the water level. For a cup float on a modern fill valve: pinch the clip on the side of the float and slide it down the valve body to lower the water level. The water level should sit about 1 inch below the top of the overflow tube.

How much water does a running toilet waste?

A slow leak through a faulty flapper can waste 20–30 gallons per day. A constantly running toilet — where water flows continuously into the overflow tube — can waste 200 gallons or more per day. At average U.S. water rates, a running toilet adds $50–$200 to your monthly water bill.

Can I fix a running toilet without turning off the water?

You should turn off the water supply valve (the oval handle on the wall behind and below the toilet) before working inside the tank. If the valve is stuck or corroded, you can work quickly with the water on for minor adjustments, but replacing the flapper or fill valve is much easier with the supply off.

When should I replace the entire fill valve instead of just adjusting it?

Replace the fill valve if: the toilet still runs after adjusting the float, the fill valve makes a hissing or screaming noise during filling, the valve takes more than 3 minutes to fill the tank, or the valve is more than 10 years old. A new fill valve costs $10–$20 and takes about 20 minutes to install.

How do I fix a toilet that keeps running after flushing?

A toilet that keeps running after flushing has one of three problems: (1) Flapper not sealing (most common, 80% of cases): the rubber flapper at the bottom of the tank is worn or warped and not seating against the flush valve. Test: put a few drops of food coloring in the tank. Wait 10 minutes without flushing. If color appears in the bowl, the flapper is leaking. Fix: replace the flapper ($5–$12 at any hardware store). Turn off the water supply valve, flush to empty the tank, unhook the old flapper from the two side posts, and snap the new one on. Takes 5 minutes. (2) Float set too high: water fills past the overflow tube and drains continuously into the bowl. You'll see water trickling into the bowl and hear a faint running sound. Test: look inside the tank — if water is at or above the top of the overflow tube, the float is too high. Fix: adjust the float arm down (older ball float) or turn the adjustment screw on the fill valve (newer tower fill valves) to lower the water level to 1 inch below the top of the overflow tube. (3) Fill valve worn: if adjusting the float doesn't stop it and the flapper is good, the fill valve is failing. Replace the fill valve ($12–$25, 20 minutes of work). Complete toilet repair kits (flapper + fill valve + supply line) cost $20–$30 and replace everything at once — worth doing if the toilet is over 10 years old.

How much does a plumber charge to fix a running toilet?

A plumber charges $100–$250 to fix a running toilet depending on what needs replacing: Flapper replacement only: $75–$150 (labor minimum call charge — the part itself costs $5). Fill valve replacement: $100–$200 (30–45 minutes of work). Complete toilet rebuild (flapper + fill valve + handle): $150–$300. These repairs are simple enough that most homeowners should DIY them — a complete rebuild kit costs $25–$40 at any hardware store and the total repair takes 30–60 minutes with no special tools beyond an adjustable wrench. The only scenario worth hiring a plumber for toilet running: if the shutoff valve behind the toilet is corroded or won't close, or if the toilet is leaking at the base (wax ring failure) — both require more involved work. For a straightforward flapper or fill valve issue, the labor cost of hiring a plumber is 10–20× the material cost.

Fix a running toilet by replacing the flapper — a $5–$10 repair that solves 90% of running toilets in under 10 minutes. Shut off the water at the wall valve, flush to empty the tank, unhook the old flapper, snap on the new one (universal flappers fit most toilets), and turn the water back on. If the toilet still runs after the flapper, the fill valve needs replacing ($10–$25 part). A running toilet wastes 200+ gallons per day — fix it immediately.

A running toilet is one of the most common and most wasteful household plumbing problems. The good news: 90% of running toilet problems are caused by a $5–$15 part that you can replace yourself in under 30 minutes. This guide walks you through diagnosing exactly what’s wrong and fixing it for good.

What You Need

Before you start, gather these tools and materials. Most of the parts are inexpensive and available at any hardware store or online.

• Toilet flapper replacement ($5–$10 for a universal flapper)
• Toilet fill valve replacement kit ($10–$20 for a complete adjustable fill valve)
• Toilet repair kit all-in-one ($15–$25 for a flapper and fill valve combo)
• Adjustable pliers or channel-lock pliers for disconnecting the supply line
• Food coloring dye tabs for toilet testing ($5–$8 for a pack of leak detection tablets)
• Toilet supply line replacement ($8–$15 if your existing supply line is old or corroded)

A dry towel and a small bucket are also helpful for soaking up residual water in the tank.

How a Toilet Works (Quick Overview)

Understanding the toilet’s basic anatomy makes diagnosis much easier. Inside the tank you’ll find three main components:

The fill valve (also called the ballcock) controls the water supply into the tank. When you flush, the water level drops, the float drops with it, and the fill valve opens to let water back in. When the water reaches the correct level, the float rises and shuts the fill valve off.

The flapper is the rubber seal at the bottom of the tank that holds water in until you flush. Pressing the flush handle lifts the flapper, releases the water into the bowl, then the flapper drops back down to seal the tank while it refills.

The overflow tube is a vertical standpipe inside the tank that acts as a safety drain. If the fill valve fails to shut off and the water level rises too high, water spills down the overflow tube into the bowl rather than overflowing the tank onto the floor.

When a toilet runs continuously, it means water is either leaking past a faulty flapper into the bowl, or the fill valve isn’t shutting off and water is running down the overflow tube.

Step 1: Diagnose the Problem

Remove the tank lid and set it somewhere safe — it’s heavy porcelain and breaks easily.

Look at the water level. Is the water level at or above the top of the overflow tube? You may actually see water trickling down into the tube. If so, the fill valve isn’t shutting off, or the float is set too high. This is an overflow problem, not a flapper problem — go to Step 4.

If the water level is below the overflow tube, the water is leaking through the flapper. Confirm with the food coloring test: put a few drops of food coloring or a dye tablet in the tank and wait 10 minutes. If color seeps into the bowl without flushing, the flapper is leaking.

Listen carefully. A running toilet often makes a quiet hissing sound. If the hissing comes from the valve area and you can see water running into the overflow tube, that’s a fill valve or float issue. If the hissing is quieter and the tank slowly loses water with no visible overflow, that’s a flapper issue.

Step 2: Fix a Leaking Flapper

The flapper is the most common cause of a running toilet, and it’s also the easiest fix. Flappers are made of rubber, and they degrade over time — typically every 3–7 years — due to chlorine in the water supply, mineral buildup, and simple aging.

Turn off the water supply. The shut-off valve is on the wall behind the toilet near the floor. Turn it clockwise until it stops. Flush the toilet to empty the tank.

Remove the old flapper. The flapper has two “ears” or loops that hook onto pegs on either side of the overflow tube. Unhook these ears and disconnect the chain from the flush handle arm. Inspect the old flapper — if it’s discolored, stiff, warped, or has a rough or pitted sealing edge, it’s definitely the problem.

Check the flush valve seat. Run your finger around the circular seat where the flapper seals. It should feel smooth. If it’s rough, gritty, or has a visible crack or pit, the seat is damaged and the toilet will keep leaking even with a new flapper. In that case, you’ll need to replace the entire flush valve assembly — or you can try an oversized flapper designed to span small seat imperfections.

Install the new flapper. Most flappers are universal and will fit any standard toilet. Hook the ears over the pegs on both sides of the overflow tube. Attach the chain to the same hole on the flush arm where the old chain connected. Chain length matters: there should be about 1/2 inch of slack when the flapper is seated. Too tight and the flapper won’t seal; too loose and the chain can get caught under the flapper.

Turn the water back on and test. Watch the flapper seat as the tank fills. Once full, the toilet should stop running completely. Flush several times to confirm the new flapper seats correctly each time.

Step 3: Adjust or Replace the Float

If the water level is correct and the flapper is new but the toilet still runs, or if the water level is at or above the overflow tube, the float needs adjustment.

Ball float adjustment (older toilets with a ball on an arm): The float is a hollow ball attached to a horizontal arm. If the ball is cracked or waterlogged, it sinks and can’t shut off the valve — replace it. If the ball is intact, bend the float arm gently downward to lower the target water level. Some ball float assemblies have an adjustment screw instead — turn it clockwise to lower the float.

Cup float adjustment (modern fill valves with a cylindrical float on the valve body): Find the adjustment clip or screw on the side of the float. Pinch the clip and slide the float body downward on the valve shaft to lower the water level. On some models, there’s a small adjustment screw at the top of the fill valve — turn it counterclockwise to lower the water level.

Target water level: The water should sit about 1 inch below the top of the overflow tube. There’s usually a water line marked inside the tank. Adjust the float, flush, and let the tank refill to confirm the level is correct.

Step 4: Replace the Fill Valve

If float adjustment doesn’t stop the running, or if the fill valve makes noise, takes too long to fill, or has visible corrosion or mineral scale, replace the entire fill valve. This is a 20-minute job.

Turn off the water supply and flush the toilet to empty the tank. Use a sponge or small cup to remove any remaining water in the bottom of the tank.

Disconnect the supply line. Under the tank, unscrew the supply line from the fill valve shank. Have a small bucket ready — there will be residual water in the line.

Remove the old fill valve. From inside the tank, lift or unscrew the float assembly if it’s separate. Under the tank, unscrew the large plastic nut holding the fill valve to the tank. Lift the old valve straight up and out.

Measure and set the new fill valve height. Most modern fill valves (like the Fluidmaster 400A) are adjustable in height. Before installing, hold the new valve next to the overflow tube — the top of the valve’s cap should sit about 1 inch above the top of the overflow tube. Twist the valve body to adjust the height.

Install the new fill valve. Insert the threaded shank through the hole in the tank bottom. From underneath, hand-tighten the plastic nut — then snug it just 1/4 turn more with pliers. Don’t overtighten; the tank is ceramic and can crack.

Connect the fill tube. The new valve comes with a flexible fill tube — attach one end to the valve outlet and the other end to the clip that goes over the overflow tube (this refills the bowl after each flush).

Reconnect the supply line and turn the water on. Watch for leaks at the base of the valve and at the supply line connection. Adjust the float setting on the new valve to set the correct water level.

Step 5: Fix a Running Toilet After Flushing

Sometimes the toilet runs for 15–30 seconds after flushing, then stops — this is usually normal. But if it runs for longer, there are a few possible causes:

Chain too short or kinked. If the chain is too short, the flapper can’t fully seat when the handle is released. The chain may also get kinked or tangled, holding the flapper slightly open. Adjust the chain length or replace a kinked chain.

Flapper not compatible with your toilet model. Some toilets require brand-specific flappers (Kohler, American Standard, and Toto are the main brands with proprietary designs). If a universal flapper isn’t sealing properly, check the toilet model number (usually stamped inside the tank or on the back of the bowl) and order the correct OEM flapper.

Fill valve flow rate too low. If the fill valve takes more than 3 minutes to fill the tank, something is partially blocking the supply. Check the shut-off valve is fully open, check the supply line for kinks, and check the fill valve’s intake screen for sediment (rinse it under a faucet).

Step 6: When to Call a Plumber

Most running toilet repairs are DIY-friendly, but there are situations where calling a plumber makes sense:

• The flush valve seat is cracked or severely pitted and needs full replacement
• The tank has a visible crack that’s causing leaks
• The toilet is more than 20 years old and has recurring issues — consider replacing the entire toilet
• Water is leaking from the base of the toilet (not the tank) — this indicates a wax ring failure, which requires removing the toilet
• The shut-off valve is frozen and you can’t turn the water off

A plumber will typically charge $100–$200 to repair a running toilet, or $150–$400 to replace the toilet if it’s beyond repair.

Cost to Fix a Running Toilet

Repair	DIY Cost	Pro Cost
Flapper replacement	$5–$10	$75–$150
Fill valve replacement	$10–$20	$100–$175
Complete tank rebuild kit	$15–$30	$125–$200
Flush valve seat repair	$15–$40	$150–$250
Full toilet replacement	$100–$400	$300–$800

The water savings alone justify the repair. A toilet running at 200 gallons per day costs roughly $20–$30 per month extra on your water bill — meaning a $10 flapper pays for itself in days.

Maintenance Tips to Prevent Future Running

Test your toilet annually. The food coloring test takes two minutes and catches silent leaks before they waste hundreds of gallons.

Replace flappers proactively. Flappers last 3–5 years in chlorinated municipal water. If yours is older, replace it even if it isn’t obviously leaking yet — it’s a $5–$10 part.

Check water pressure. Water pressure above 80 PSI can wear out flappers and fill valves faster. If you have high water pressure, a pressure regulator (PRV) installed on the main supply line extends the life of all your plumbing fixtures.

Avoid in-tank cleaning tablets with bleach. Continuous-release chlorine tablets in the tank accelerate rubber flapper degradation. Use bowl rim tablets instead, or clean the toilet manually.

Related Reading

• How to Fix Low Water Pressure
• How to Install a Toilet
• How to Replace a Shower Head
• How to Shut Off Water to Your House
• Handyman Cost Guide — when a plumber is more than you need
• Plumber Cost — what to expect if you call a pro
• How to Fix a Broken Shower Diverter — repair a diverter that won’t redirect water from tub to shower
• How to Fix a Broken Toilet Handle — replace a broken or disconnected flush handle while you have the tank lid off
• How to Fix a Broken Toilet Seat — replace a cracked or loose toilet seat in the same visit
• How to Fix a Broken Toilet Wax Ring — replace a leaking wax ring at the toilet base while the toilet is already being serviced
• How to Fix a Broken Water Pressure Regulator — replace a failing PRV if high water pressure is causing your toilet to run constantly