Toilet Keeps Running? Find the Cause and Fix It

A toilet that keeps running almost always has one of three problems: a flapper that no longer seals, a fill valve that won't shut off, or a water level set too high. Most of the time you can tell which one in about ten minutes with a little food coloring and a look inside the tank. Below is how to diagnose it, fix the common causes, and recognize the point where a plumber is the cheaper call.

TL;DR

• The most common culprit is a worn-out flapper, the rubber seal at the bottom of the tank, according to the Saving Water Partnership.
• Drop food coloring in the tank and wait at least 10 minutes without flushing. Color in the bowl means the flapper is leaking.
• If the tank fills and water keeps flowing into the overflow tube, look at the float and fill valve instead.
• Don't wait on it: NYC's Department of Environmental Protection says a stuck-open fill valve can waste up to 4,000 gallons a day.
• If the parts are fine and it still runs, or water is on the floor, shut off the supply and call a licensed plumber.

Table of Contents

• What a running toilet is actually doing
• Signs your toilet is leaking, even when it's quiet
• Step 1: Do the two-minute dye test
• Step 2: Check the handle and chain
• Step 3: Inspect and replace the flapper
• Step 4: Check the water level, float and fill valve
• Quick diagnosis table
• What happens if you ignore it
• When to stop and call a plumber
• Our perspective: fix the small thing before it becomes the big thing
• Need a hand in Rio Rancho, Albuquerque or Corrales?
• Preventing the next running toilet
• FAQ
• Sources

What a running toilet is actually doing

Your toilet tank is a simple machine. When you flush, the flapper lifts and the tank empties into the bowl. The flapper drops back down and seals the opening, and the fill valve refills the tank until a float tells it to stop. Any part that fails to do its job keeps water moving.

There are really two ways the loop goes wrong:

1. Water leaks out of the tank into the bowl. The water level drops, so the fill valve opens to top it off. You hear the toilet refill on its own every few minutes, or you hear a faint hiss. This is the "phantom flush."
2. Water keeps coming in after the tank is full. The fill valve or float doesn't shut off, so water spills into the overflow tube and runs down the drain nonstop.

Korky, a toilet repair parts maker, draws the same line: recurring refills usually mean water is escaping past the flapper or flush seal, while flow after the tank is full points toward the fill valve. Knowing which of the two you have saves you from buying the wrong part.

Signs your toilet is leaking, even when it's quiet

Not every running toilet is loud. The Saving Water Partnership lists warning signs that include:

• A tank that refills constantly or between flushes
• Water dribbling into the bowl when nobody has flushed
• A handle you have to jiggle to make it stop
• A flapper that looks worn or warped

If your toilet runs only now and then, that is a clue in itself. According to the same source, an aging flapper may seal after some flushes and not after others. That is why "toilet running intermittently" is so often a flapper problem that hasn't fully failed yet.

Step 1: Do the two-minute dye test

Before you touch anything, confirm where the water is going.

1. Remove the tank lid and set it somewhere safe.
2. Add a teaspoon of food coloring, or several drops, to the tank water. Dark colors like blue or red are easiest to see.
3. Don't flush. Wait at least 10 minutes. NYC DEP suggests 10 to 15 minutes, and the Saving Water Partnership says at least 10.
4. Look in the bowl. If color shows up, tank water is leaking past the flapper or flush valve seat. If the bowl water is clear, the leak is somewhere else, most likely the fill valve.

Rinse the tank afterward and flush a couple of times so the dye doesn't linger.

A second test: mark the water level

NYC DEP also describes a level-marking method. Mark the water level in the tank, flush, and watch it refill. If the level rises above your mark and then falls, suspect a flapper leak. If it rises from below the mark to above it, suspect a faulty fill valve.

Fluidmaster gives a version you can do with the supply off: mark the full level, shut off the water at the valve, and wait 10 to 15 minutes. If the level drops, replace the flapper. If it still drops after a new flapper, the flush valve itself may need replacing.

Step 2: Check the handle and chain

The cheapest fix is often the first one. Look at the chain that connects the flush handle's arm to the flapper.

• Too long: the chain can slip under the flapper and hold it open a crack.
• Too short: it can pull on the flapper and keep it from seating fully.
• Loose handle: the lever may not drop back to rest.

Portland Water Bureau lists a chain that is too long or short, a misaligned flapper, or a loose handle as causes of running. Its repair guide says to adjust the chain and tighten the handle nut, replacing the handle if needed. American Standard's guidance says the chain should have about a quarter inch of slack when attached to the trip lever. Think "just enough play to let the flapper close," not a taut line and not a loose loop.

Step 3: Inspect and replace the flapper

If the dye test showed color in the bowl, the flapper is your suspect. Over the years rubber hardens, warps, or gets coated with grit, and it stops sealing the opening. The Saving Water Partnership calls a worn-out flapper the usual cause of a running toilet.

Here is how to deal with it:

1. Shut off the supply valve behind or beside the toilet (turn it clockwise).
2. Flush to drain the tank.
3. Unhook the flapper from the overflow tube pegs and the chain from the lever.
4. Wipe the flush valve seat, the ring the flapper sits on, with a damp cloth. Mineral film or grit here can stop a good flapper from sealing.
5. Press on the old flapper. If it feels stiff, slimy, or misshapen, replace it.
6. Take the old one to a hardware store to match the size and style, since flappers come in different sizes and shapes. Install the new one, reconnect the chain with a little slack, and reopen the supply.
7. Repeat the dye test to confirm it's sealed.

If you're looking at a toilet that's decades old and needs more than a flapper, a step-by-step guide to replacing a toilet shows what a full swap involves, which helps you decide whether more repairs make sense.

A note on in-tank cleaners

Those drop-in bleach tablets are convenient, but they can shorten a flapper's life. NYC DEP says chlorine in-tank cleaners can corrode rubber flappers and other tank parts, especially when a toilet isn't flushed for a long period. If you have a flapper that keeps failing early, stop using them.

Step 4: Check the water level, float and fill valve

If the dye test came back clear, or the tank fills to the top and water keeps flowing, look at where the water stops.

Look for the overflow tube, the open vertical pipe in the center of the tank. The Saving Water Partnership says water should stop at the marked fill line or below the top of the overflow tube. Water above that can make the toilet run continuously. Specific guidance on how far below varies by source:

Many toilets also have a fill line marked inside the tank. If yours does, follow the manufacturer's mark. Portland adds that a level set too high spills into the tube, while one set too low can weaken your flush.

Adjusting the float

• Cup-style float on the fill valve: turn the adjustment screw or squeeze the clip on the rod and slide the float down.
• Ball-and-arm float: gently bend the arm down a bit, or turn the adjusting screw if there is one.

Flush and watch the refill. Korky says that if the tank is full but water keeps flowing, the float may be set too high, clogged with debris, or failing. Adjusting it, cleaning it, or replacing the fill valve handles that condition.

Cleaning or replacing the fill valve

Sediment is a common troublemaker. One toilet maker notes that leaking or constant running can come from debris lodged in the fill valve cap, which keeps the valve from closing. Check your tank for grit and flush the valve per the manufacturer's instructions, which usually means lifting the cap and letting a burst of water rinse it out with a cup held over the top.

If cleaning doesn't work, replace the valve. True Value's repair walkthrough covers the sequence: shut off the supply, flush and dry the tank, remove the supply slip nut and the fill valve locknut, disconnect the overflow tube from the refill tube, and swap in the new valve. A universal fill valve is inexpensive, but a stubborn nut or a cracked supply line is where a quick repair can become a messy one.

Quick diagnosis table

What happens if you ignore it

A running toilet doesn't flood your house, which is why many people live with it for months. It does quietly cost you. NYC DEP says an open fill valve can pass 3 to 5 gallons per minute, which adds up to as much as 4,000 gallons a day. A smaller flapper leak wastes less, but it never stops. It recommends prompt repair and testing each toilet once a year.

In New Mexico, where many of us pay close attention to every gallon, a toilet that cycles all night is worth fixing the same weekend you notice it. And over time, water constantly trickling over parts can wear them faster, so the repair gets bigger the longer you wait.

When to stop and call a plumber

Plenty of running toilets are a 20-minute job. Some aren't. Call a licensed plumber if:

• You've replaced the flapper and fill valve and it still runs. The flush valve seat may be pitted or cracked, or the fault may sit elsewhere in the fixture.
• There's water on the floor. Fluidmaster says to shut off the supply right away and check the tank. Tank-bottom leakage may require replacing the tank bolts and washers, and a leak at the base can point to a failed wax ring.
• The shutoff valve won't close or is corroded. Forcing an old valve can turn a small repair into a burst line.
• You have several fixtures acting up. A pressure problem can be the real cause. NYC DEP lists water-pressure changes that hold the fill valve open among the causes of toilet leaks. If you also hear banging pipes, see our guide to water hammer fixes.
• You aren't comfortable with the repair. The NYC agency recommends calling a licensed master plumber if you can't make the repairs yourself, and Portland Water Bureau likewise advises homeowners to know their limits.

If your water bill is high but you can't find the source, the toilet may not be the only leak. Our post on leak detection methods explains how a pro finds hidden ones.

Our perspective: fix the small thing before it becomes the big thing

After more than 38 years of plumbing in New Mexico homes, we see the same pattern with running toilets. People call us after they have already tried two or three parts, and often the original problem was a flapper that was never seated properly or a chain with too much slack. Our advice is to do the dye test first. It takes the guesswork out, and it keeps you from spending money on a fill valve when the real culprit is a $10 seal.

We also tell homeowners that a running toilet is a good moment to look at the whole bathroom. If the toilet is old, the supply line is corroded, or the shutoff valve doesn't turn, replace those at the same visit rather than coming back in six months. Our plumbers are licensed, we leave your bathroom clean, and when you call you talk with a local person, not a phone menu.

The best repair is the one that holds. If a DIY fix is within your comfort zone, go for it. If you reach the point where you're guessing, call us and we'll sort it out.

— Aaron Waller, General Manager

Need a hand in Rio Rancho, Albuquerque or Corrales?

If you've gone through the checklist and the toilet is still running, or you'd simply rather have it done right the first time, our team handles toilet and faucet repairs, leak detection and full plumbing repairs for homeowners across the area. You can see everything we do on our plumbing repair and leak detection services page, or start from our home page to book an appointment online. Planning a bigger update while we're there? Take a look at our bathroom remodel overview.

Preventing the next running toilet

• Test each toilet once a year with food coloring. It's the habit NYC DEP recommends.
• Skip chlorine tank tablets, which can corrode rubber parts.
• Replace the flapper every few years as cheap insurance, especially when you see a film or warping.
• Keep the tank clean. Grit and sediment can damage the flush valve and clog the fill valve, as NYC DEP notes.
• Learn where your shutoff valves are and turn them occasionally so they don't seize.

FAQ

How do you fix a toilet that keeps running?

Turn off the supply, flush to drain the tank, and check the handle, chain and flapper first. Adjust the chain slack, clean the flapper seat or replace the flapper, then set the float so the water stops below the overflow tube. Turn the water back on and test-flush.

What is the most common cause of a constantly running toilet?

A worn-out flapper. As the rubber deteriorates it stops sealing the flush valve, and tank water slips into the bowl. That makes the fill valve open again and again to refill the tank.

Why does my toilet run on and off by itself?

That's usually a slow leak from the tank into the bowl, which drops the water level until the fill valve kicks on. An aging flapper may seal after some flushes and not others, so the running can seem random. A dye test will confirm it.

Why is water constantly trickling into my toilet bowl?

Trickling into the bowl usually means tank water is getting past the flapper or the overflow tube is receiving water from a fill valve that won't shut off. Check the water level against the overflow tube, then do the dye test to see which one it is.

Is a running toilet an emergency?

Not usually, but it shouldn't wait. If water is reaching the floor, shut off the supply valve and call a plumber. Otherwise, fix it soon to avoid wasting water and paying for it.

Sources

• Toilet Leaks, Saving Water Partnership
• Toilet Leak Detection, NYC Department of Environmental Protection
• How to find and fix a toilet leak, Portland Water Bureau
• Toilet running after flush, American Standard
• Constantly Running Toilet: Common Causes and Solutions, Fluidmaster
• How to Fix a Running Toilet, Korky
• DIY Toilet Repair, True Value

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