How to Fix a Running Toilet (The Flapper Fix Takes 5 Minutes)

A running toilet wastes up to 200 gallons of water per day. That's not just annoying — it's expensive. At average water rates, a continuously running toilet can add $50-100 per month to your water bill. Over time, it's one of the most costly problems you can have that's also one of the easiest to fix yourself.

In about 90% of cases, the problem is a $5 part that takes 5 minutes to replace. Here's how to diagnose the issue and fix it without calling a plumber.

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Why Is My Toilet Running?

A toilet runs when water continuously leaks from the tank into the bowl. There are three common causes, and you can diagnose the problem in about 30 seconds.

The food coloring test: Put 5-10 drops of food coloring in the tank (not the bowl). Wait 15 minutes without flushing. If colored water appears in the bowl, you have a flapper leak — the most common issue.

The three usual suspects:

1. Worn flapper (most common) — The rubber flapper at the bottom of the tank doesn't seal properly, allowing water to continuously leak into the bowl. The fill valve keeps running to replace the lost water.
2. Float set too high — The float (ball or cup) is set above the overflow tube, so water continuously drains through the overflow.
3. Faulty fill valve — The fill valve doesn't shut off when the tank is full, causing continuous filling and overflowing.

Let's fix each one.

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How Do You Replace a Toilet Flapper?

This is the fix for 90% of running toilets. A universal toilet flapper costs $5-8 and fits most standard toilets.

Steps:

1. Turn off the water supply — Turn the shut-off valve behind the toilet clockwise until it stops. It's the knob on the wall near the floor.
2. Flush the toilet — This empties the tank so you can work inside it. Hold the handle down to drain as much water as possible.
3. Remove the old flapper — Unhook the flapper chain from the flush lever. Then unhook the flapper ears from the pegs on either side of the overflow tube. The flapper pulls right off.
4. Take it to the store — Bring the old flapper with you to match the size. Or buy a universal flapper that adjusts to fit most toilets.
5. Install the new flapper — Hook the flapper ears onto the overflow tube pegs, reconnect the chain to the flush lever. The chain should have about half an inch of slack — too tight and the flapper won't seal, too loose and it won't lift when you flush.
6. Turn the water back on — Turn the shut-off valve counter-clockwise. Let the tank fill.
7. Test — Flush a couple of times and watch for proper sealing. The running should stop.

That's it. Five minutes, one inexpensive part, no tools required. This is the kind of repair covered in our guide to fixing a running toilet, and it's one of the first DIY skills every homeowner should learn.

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How Do You Adjust the Float?

If the food coloring test didn't show a leak (water stays clear in the bowl after 15 minutes), but you can see water flowing into the overflow tube inside the tank, the float is set too high.

For a ball float (older toilets):

The float is a ball on the end of a metal arm. Gently bend the arm downward about half an inch. This lowers the water level so it stops below the overflow tube. Flush and check — the water should stop about 1 inch below the top of the overflow tube.

For a cup float (newer toilets):

The float is a cylinder that rides up and down on the fill valve. Find the adjustment screw or clip on the side of the float. Turn the screw counter-clockwise (or squeeze the clip and slide the float down) to lower the water level. A half-inch adjustment is usually enough.

After adjusting, flush and watch. The water should fill to about 1 inch below the overflow tube and stop cleanly.

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When Do You Need to Replace the Fill Valve?

If the flapper is fine and the float is set correctly, but water keeps running, the fill valve itself is likely faulty. The fill valve is the tall mechanism on the left side of the tank that controls incoming water.

Signs of a bad fill valve:

• The valve hisses or vibrates constantly
• Water trickles into the tank non-stop regardless of the water level
• The valve doesn't fully shut off after the tank fills
• Adjusting the float doesn't change anything

A universal fill valve replacement costs $8-15 and takes about 15-20 minutes to install. It's slightly more involved than a flapper swap but still well within DIY territory.

Basic steps:

1. Turn off water and flush to empty the tank
2. Place a towel under the tank — some water will drip
3. Disconnect the water supply line from the bottom of the fill valve
4. Unscrew the lock nut under the tank and pull the old fill valve out from inside
5. Adjust the new fill valve to the correct height (instructions are on the package)
6. Insert it, tighten the lock nut, reconnect the water supply
7. Turn on the water and adjust the float to set the correct water level

If you already have a basic tool kit, you have everything you need. The only tool required is a pair of adjustable pliers.

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How Much Water Does a Running Toilet Waste?

A running toilet wastes a staggering amount of water:

• Slow leak (flapper barely failing) — 30-50 gallons per day
• Moderate leak (visible ripples in bowl) — 100-200 gallons per day
• Full-on running (you can hear it) — 200+ gallons per day

At average U.S. water rates of $4-5 per 1,000 gallons, even a moderate leak costs $12-30 per month. Over a year, that's $150-360 wasted on a problem that costs $5-15 to fix. It's one of the easiest ways to lower your water bill.

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Frequently Asked Questions

Why does my toilet run intermittently (phantom flushes)?

Intermittent running — where the toilet randomly runs for a few seconds every 10-30 minutes — is caused by a slow flapper leak. The tank slowly loses water through the flapper seal until the fill valve kicks in to top it off. Replace the flapper and the phantom flushes stop.

Can I use a different brand of flapper?

Yes. Universal flappers fit most standard toilets. The two main sizes are 2-inch (older toilets) and 3-inch (newer toilets). Bring your old flapper to the hardware store to match the size, or buy a universal adjustable flapper that fits both.

How long do toilet flappers last?

Most flappers last 3-5 years before the rubber deteriorates enough to cause leaks. Chlorine tablets or bleach-based toilet bowl cleaners can degrade flappers faster — sometimes in less than a year. If you use in-tank cleaning tablets, consider switching to a chlorine-resistant flapper.

Should I replace the whole toilet if it keeps running?

Almost never. The internal parts (flapper, fill valve, flush valve) are all inexpensive and replaceable. Replacing the toilet is only warranted if the porcelain is cracked, the toilet is older than 20 years and uses excessive water per flush (3.5+ gallons vs modern 1.28 gallons), or the flush valve seat itself is corroded.

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Fix It Today

Every day you wait is money flowing down the drain — literally. Walk to your toilet right now, take the lid off the tank, and do the food coloring test. If the color shows up in the bowl, go buy a $5 flapper and fix it today. It's one of the simplest home repairs that exists, and it pays for itself within the first week.