Running Toilet? Call Plumber Near You — Same-Day Fix

A toilet that keeps running is one of those problems that's easy to ignore because it's not causing visible water damage — until you see your water bill. A running toilet wastes 200–400 gallons a day. At average US water rates, that's $50–$100 a month disappearing down the drain for a problem that costs less than $15 to fix.

The good news is that a running toilet is almost always caused by one of three components: the flapper, the float, or the fill valve. Open the tank lid and you can usually identify the culprit in under two minutes.

Understanding Your Toilet Tank: 60-Second Anatomy

You don't need to be a plumber to fix this. Here's the quick overview of what's in your toilet tank:

• Flapper: The rubber seal at the bottom of the tank. It lifts when you flush, lets water rush into the bowl, then closes to hold the tank while it refills. Most running toilet problems start here.
• Fill valve (ballcock): Attached to the water supply line. Lets water into the tank after a flush and shuts off when the water reaches the correct level. A failed fill valve won't shut off properly.
• Float: Controls when the fill valve shuts off. On modern toilets it's a float cup that rides up and down on the fill valve. On older toilets it's a plastic ball on an arm (ballcock style). If the float is set too high, water keeps rising into the overflow tube.
• Overflow tube: A vertical tube in the center of the tank. If the water level rises above it, water constantly flows into the bowl through this tube — which is what causes the constant running sound.
• Flush handle and chain: The chain connects the handle to the flapper. If the chain is too long, it can get caught under the flapper and prevent a proper seal.

Step 1: The Dye Test — Is Your Flapper Leaking?

This is the fastest way to know if your flapper is the problem. Drop a few drops of food coloring (or a toilet dye tablet) into the tank. Do NOT flush. Wait 15 minutes.

Check the toilet bowl. If you see color in the bowl water — the flapper is leaking. Water is seeping past the seal and into the bowl, which triggers the fill valve to refill the tank constantly.

If there's no color in the bowl, the flapper is sealing fine. Move to Step 2.

Step 2: Check the Water Level Relative to the Overflow Tube

Remove the tank lid and look at the water level. It should sit approximately 1 inch below the top of the overflow tube. If the water level is at or above the top of the overflow tube, water is constantly draining into the bowl through the overflow — causing the running sound.

This means the float is set too high. The fill valve is putting too much water into the tank before shutting off.

How to Fix a Leaking Flapper

This is a 10-minute job that requires no tools and costs $5–$15.

1. Turn off the water supply valve behind the toilet (turn clockwise)
2. Flush the toilet to drain the tank
3. Unhook the flapper chain from the flush handle lever
4. Slide the flapper's ear loops off the pegs on the overflow tube (or unsnap if it has a neck mount)
5. Take the old flapper to the hardware store to match it, or buy a universal flapper (Korky or Fluidmaster brands are reliable)
6. Snap the new flapper onto the overflow tube pegs
7. Reconnect the chain — leave 1/2 inch of slack so the flapper can close fully but still lift when the handle is pressed
8. Turn the water supply back on and test

Check that the flapper closes completely and the tank fills to the correct level. Do the dye test again after 15 minutes to confirm the seal is good.

Why Flappers Fail

Rubber flappers degrade naturally over 5–8 years. Chlorine and minerals in tap water accelerate this. A warped, cracked, or stiff flapper can't create a full seal against the flush valve seat. Mineral buildup on the valve seat itself can also prevent the flapper from closing — clean the seat with white vinegar and a cloth before installing the new flapper.

How to Adjust or Replace the Float

Adjusting a Float Cup (Modern Toilets)

Modern toilets have a float cup that rides on the fill valve shaft. To lower the water level, pinch the adjustment clip on the float cup and slide it down. Some models have an adjustment screw at the top of the fill valve — turn it clockwise to lower the water level.

After adjusting, flush the toilet and watch where the water settles. It should stop about 1 inch below the top of the overflow tube.

Adjusting a Ball Float (Older Toilets)

Older toilets have a large plastic ball on the end of a metal or plastic arm. Bending the arm slightly downward lowers the float, which causes the fill valve to shut off sooner. Some have an adjustment screw at the valve end of the arm instead.

How to Replace a Failing Fill Valve

If adjusting the float doesn't stop the running, or if you can hear the fill valve hissing even when the tank is full, the fill valve itself needs replacing.

A universal fill valve (Fluidmaster 400A is the industry standard, costs about $12) works in virtually all toilets. The replacement takes about 20–30 minutes:

1. Turn off the supply valve and flush to drain the tank
2. Disconnect the supply line from the bottom of the fill valve
3. Unscrew the locknut on the underside of the tank (hand-tight, or pliers)
4. Pull the old fill valve straight up and out
5. Set the height on the new fill valve per instructions (should be 1 inch above the overflow tube)
6. Insert the new valve, secure the locknut, reconnect the supply line
7. Connect the refill tube to the overflow tube
8. Turn on the supply, let the tank fill, and adjust the float until water stops 1 inch below the overflow tube

Other Running Toilet Causes to Check

Flapper Chain Too Long

If the chain is too long, it can get caught under the flapper, leaving a small gap. This causes intermittent running. Shorten the chain by hooking it a few links higher on the handle lever.

Flush Valve Seat Damage

The flush valve seat is the ring at the bottom of the tank that the flapper seals against. If it's cracked, warped, or has deep mineral deposits, no flapper will seal properly against it. This requires replacing the flush valve — a more involved repair that usually warrants a plumber.

Fill Valve Shuts Off But Toilet Still Runs

If the fill valve shuts off but you still hear running, the water is coming from a different source — possibly a cracked overflow tube or a flush valve seat issue. This is harder to self-diagnose and a plumber can identify it quickly.

When to Stop DIYing

Call a plumber if:

• You replaced the flapper and fill valve and the toilet still runs
• You see water on the floor around the toilet base — this suggests a wax ring problem, not a tank issue
• The flush handle is loose or unresponsive
• The toilet also has a weak flush — see our guide on toilet not flushing properly for combined issues
• You have an older toilet and are uncomfortable working with the ballcock mechanism

A licensed plumber can diagnose and repair any toilet issue same day. If your toilet also has a drainage problem or you're hearing gurgling from the bathroom drain, mention both when you call — they're often related.

Need a local plumber now? Connect with a licensed plumber in your area for same-day service.

Cost to Fix a Running Toilet

Fix	Estimated Cost
Flapper replacement (DIY)	$5–$15
Fill valve replacement (DIY)	$10–$20
Complete toilet rebuild kit (DIY)	$20–$40
Plumber: flapper/fill valve replacement	$100–$200
Plumber: flush valve replacement	$200–$350
Wasted water (running toilet, 1 month)	$50–$100

Frequently Asked Questions