Why Does My Toilet Keep Running?

by the Berry team · Updated October 20, 2026

A toilet that keeps running almost always has a worn flapper, a chain that is too short or tangled, or a fill valve set so high that water spills into the overflow tube. All three are fixable in under an hour with parts that usually cost less than $30.

Likely causes and what they cost to fix

Ordered roughly from most to least common. Take the tank lid off and watch one flush; you can usually spot the cause by eye. The five-minute diagnosis below walks through it.

Cause	How to recognize it	DIY cost	Pro cost
Worn or warped flapper	The tank slowly drains into the bowl, then the fill valve kicks on by itself every so often. Pressing down on the flapper stops it.	DIY$5-$15	Pro$100-$200
Chain too short, too long, or tangled	The flapper does not seat fully after a flush, or the handle has to be jiggled to make it stop.	DIY$0-$5	Pro$100-$150 if it is the only issue
Water level set too high	Water keeps trickling into the top of the overflow tube, the open pipe in the middle of the tank.	DIY$0	Pro$100-$150
Failing fill valve	Hissing or a constant trickle even with the water level set correctly, or the tank refills very slowly or not at all.	DIY$10-$30	Pro$150-$300
Refill tube in the wrong spot	The small tube from the fill valve is pushed down inside the overflow pipe, siphoning water out of the tank.	DIY$0-$5 for a clip	Pro$100-$150
Worn flush valve seat or cracked overflow tube	A new flapper does not stop the leak, the seat under it feels rough or pitted, or the overflow tube is cracked below the water line.	DIY$10-$40 for a seat repair kit or new flush valve	Pro$200-$400

Ranges are typical US prices and vary with your region, your home, and the season. A pro quote for your exact job beats any range.

How to find the cause

Lift the tank lid and set it somewhere flat where it cannot fall; it is heavy and breaks easily. Then work through these in order. Most people find the problem by step three.

Look at the water level. If water is flowing over the top of the overflow tube, the level is set too high. There is usually a mark on the inside of the tank or on the overflow tube showing where the water should stop, often around an inch below the top of the tube.
Press down on the flapper. If the sound of running water stops while you hold the flapper down, the flapper is not sealing. That is either the flapper itself or the chain.
Check the chain. With the flapper closed, the chain should have a little slack, about the width of a finger. Too tight and it holds the flapper open. Too loose and it can get caught under the flapper.
Check the refill tube. The small flexible tube from the fill valve should be clipped to the top of the overflow pipe, pointing in, not pushed down inside it.
Listen to the fill valve. If the water level is correct and the flapper seals but you still hear hissing, the fill valve is not shutting off fully. Fill valves wear out and are cheap to replace.

Check for a silent leak

Some toilets leak without making noise. The tank slowly drains into the bowl and the fill valve tops it up every so often, which is when you hear a short burst of running in the middle of the night. To test for it:

Put a few drops of food coloring or a toilet dye tablet in the tank. Do not flush.
Wait 15 to 30 minutes.
If color shows up in the bowl, water is leaking past the flapper or flush valve seat.

Running toilets are one of the most common causes of a water bill that jumps for no obvious reason. A steady trickle runs 24 hours a day, so even a small leak adds up over a billing cycle.

The fixes, step by step

Adjusting the water level

Most modern fill valves have a float cup that slides up and down the valve body, with an adjustment screw or clip on the side. Lower the float so the tank stops filling below the top of the overflow tube. On older toilets with a ball float on an arm, gently bend the arm down or turn the adjustment screw on top of the valve.

Replacing the flapper

Close the shutoff valve behind the toilet and flush to empty the tank. Unhook the old flapper from the pegs on the overflow tube and from the chain. Take it to the store or check the toilet brand and model printed inside the tank, because flappers come in 2-inch and 3-inch sizes and some brands use their own design. Hook on the new one, adjust the chain, turn the water back on, and test.

Replacing the fill valve

Shut off the water, flush, and sponge out what is left in the tank. Disconnect the supply line under the tank, unscrew the plastic nut holding the old valve, and lift it out. Universal fill valves fit most toilets and include instructions for setting the height. It is about a 30 minute job for most people.

When the flapper is not the problem

If a new flapper still leaks, run a finger around the flush valve seat, the ring the flapper sits on. If it feels rough, pitted, or has mineral buildup, a seat repair kit can glue a new smooth surface over it. If the overflow tube is cracked, the flush valve needs replacing, which means removing the tank from the bowl. That is a reasonable DIY project if you are comfortable with it, and a common point where people call a plumber.

Repair or replace the toilet?

Almost every running toilet is worth repairing. The internal parts are cheap and standard. Replacement starts to make sense if the tank or bowl is cracked, if the toilet rocks or leaks at the base, or if you have been chasing repeated problems with an old toilet and want a newer, lower-flow model anyway. A new toilet installed typically runs $350-$900 depending on the toilet you choose.

When to call a pro

The tank or bowl is cracked, or water is leaking onto the floor rather than into the bowl.
The shutoff valve behind the toilet is stuck, corroded, or leaking.
You have replaced the flapper and fill valve and the toilet still runs.
The flush valve needs replacing and you do not want to pull the tank.
Several toilets in the house run or hiss at once, which can point to high water pressure. Our water pressure guide shows how to check it with a $10-$15 gauge.

What makes it worse if you wait

A running toilet wastes water every hour of every day, and the cost shows up on the water bill, plus the sewer bill if yours is based on water use.
A chain or flapper problem can get worse until the toilet runs constantly instead of now and then.
Constant running wears the fill valve faster, so a $10 fix can become two.
If water is reaching the floor, a slow leak at the base can rot the subfloor before it is obvious from above.

Common questions

Why does my toilet run for a few seconds every so often?

That is usually a silent leak. Water slowly seeps from the tank into the bowl past a worn flapper, and the fill valve refills the tank when the level drops. A dye test in the tank will confirm it, and a new flapper usually fixes it.

How much does it cost to fix a running toilet?

If you do it yourself, most fixes cost $0-$30 in parts: a flapper, a chain adjustment, or a new fill valve. A plumber typically charges $100-$300 for the same repairs, and more if the flush valve needs replacing.

Can a running toilet raise my water bill?

Yes. Because it runs around the clock, even a small leak can add noticeably to a monthly bill. If your water bill jumps without a clear reason, a running toilet is one of the first things to check.

Do I need to call a plumber for a running toilet?

Usually not. Flappers, chains, water level adjustments, and fill valves are some of the easiest home plumbing repairs. Call a plumber if the shutoff valve is stuck, the porcelain is cracked, or the toilet still runs after you have replaced the flapper and fill valve.

Not sure that's your problem? Snap a photo and Berry will tell you what it is and what it should cost.

Try Berry free Download on the App Store