Toilet keeps running?

A toilet that runs on is almost always leaking water from the tank into the bowl, or the tank is overfilling. It's usually a worn flapper or a mis-set float, and it's worth fixing soon, because a leaky toilet can waste about 200 gallons of water a day.

Not sure which one it is? Snap your toilet and we’ll narrow it down.

Is the bowl backing up instead of the tank running?

That's a clog, not a leak in the tank. Toilet clogged

Likely causes

Worn or warped flapper
Most commonEasy DIY
The toilet refills on its own every so often, or hisses between flushes. Food coloring in the tank shows up in the bowl without flushing. The flapper may feel soft, warped or slimy. A replacement flapper is an inexpensive part from a hardware store.
Part: $60–120 for a pro to replace it
Chain too short or too long
CommonEasy DIY
Too short and it holds the flapper slightly open; too long and it slips under the flapper and keeps it from sealing. The water runs until you jiggle the handle.
Float set too high
CommonEasy DIY
The water level reaches the top of the overflow tube and spills into it, so the tank keeps running and refilling. Lowering the float usually stops it.
Worn fill valve
CommonModerate DIY
A hissing or trickling sound, or the tank refilling by itself, even after the flapper and float check out. The valve doesn't shut off fully once the tank is full.
Part: $60–150 for a pro to replace it
Cracked overflow tube
Less commonModerate DIY
Water leaks out through a crack in the tall tube in the middle of the tank, even when the level is set correctly. This is part of the flush valve.
Part: $60–150 for a pro to replace the flush valve

Quick checks

The tank lid is heavy porcelain: lift it with both hands and set it down flat on a towel so it can't crack or fall on your foot. If the water won't stop, turn the shutoff valve behind the toilet clockwise to close it. Don't use chemical drain cleaner on a toilet. If water is leaking onto the floor, turn the water off and keep it away from outlets and cords.

Lift the tank lid and set it down flat on a towel. It's heavy porcelain.
Watch where the water goes. If it runs into the tall overflow tube, the float is too high; if it leaks past the flapper into the bowl, the flapper is worn.
Jiggle the handle. If the running stops, the chain is tangled or the wrong length.
Do the dye test: put a few drops of food coloring in the tank and wait without flushing. Color in the bowl means a leak, usually the flapper.
If the tank won't stop refilling, turn the shutoff valve behind the toilet clockwise until it closes.

Sharpen the read

Diagnose your toilet in seconds, for free

No account, no phone number. Fixology’s AI reads your photo and tells you what’s likely wrong, how worried to be, and whether it’s a DIY fix.

Snap one of these:

inside the tank with the lid off, showing the flapper, chain and float
the water level in the tank and the top of the overflow tube
the bowl and the floor around the base

Add a note or more photos next. Nobody calls you.

When to call a pro

You've replaced the flapper and set the float and it still runs, the fill valve or flush valve needs replacing and you aren't comfortable doing it, or water is leaking onto the floor. A plumber is $45–200 an hour, and nights and weekends add $100–300. If the bowl is backing up instead, see toilet clogged. For lifespan and upkeep, see the toilet guide.

Typical cost: HomeAdvisor puts a running toilet repair at $100–400, with a typical toilet repair at $150–391 (about $271 on average). By part, Fixr lists a pro-installed flapper at $60–120, a fill valve at $60–150 and a flush valve at $60–150. A plumber charges $45–200 an hour, and nights and weekends add $100–300. If the toilet needs replacing, expect about $175 for installation plus $90–1,500 for the toilet.

Sources: HomeAdvisor: How much does toilet repair cost? (updated June 19, 2026), Fixr: Toilet repair cost (updated January 31, 2025), EPA WaterSense: Fix a leak (the dye test and about 200 gallons a day)

After a scan, Fixology can also help you find pros near you.