A worn flapper is the most likely reason your toilet won't stop running. This rubber seal at the bottom of the tank lets water slip into the bowl, so the tank keeps refilling. Replacing it is a five-minute job with no tools. If you hear a steady hiss instead, the fill valve isn't shutting off and needs replacing.
If you've ever stood in the bathroom at 2 a.m. listening to your toilet hiss like a leaky tire, you already know the feeling. A running toilet is more than annoying. The EPA's WaterSense program estimates that a leaking toilet can waste about 200 gallons of water a day, and that shows up as a real number on your next water bill.
The good news: it's almost always one of five small parts. Here's how to spot which one, and what each fix typically costs, whether you grab a screwdriver yourself or call someone in.
How to tell which part is failing
Take the tank lid off and listen: a steady hiss means the fill valve isn't shutting off, while a tank that sits quiet and then refills itself every few minutes means water is leaking past the flapper. Homeowners often describe that second pattern as "mostly quiet but it refills itself every so often."
To confirm it, mark the water line inside the tank with a pencil, shut the valve behind the toilet, and wait 20 minutes. If the water drops below the mark, the flapper or the seat under it is leaking into the bowl. If the level holds, the fill valve is the part to replace. Set the lid flat on the floor while you work, because porcelain lids crack easily.
Runhome's guide to a toilet that won't stop running or refills itself every few minutes walks through each check in order.
1. A worn-out flapper leaks water into the bowl
A worn-out flapper is the #1 culprit behind a running toilet. The flapper is the rubber disc at the bottom of the tank that lifts when you flush and drops back down to seal. After a few years it gets stiff, warped, or crusted with mineral scale, and it stops sealing tight. Water trickles into the bowl, the tank refills to compensate, and the cycle never ends.
Check the chain before you buy anything. It needs about one link of slack so the flapper can drop flat. A chain that's too short or tangled holds the flapper open.
Quick test: put a few drops of food coloring in the tank and wait 20 minutes without flushing. If color shows up in the bowl, the flapper is leaking.
What it typically costs
- DIY: $5 to $20 for a new flapper. Yelp's cost guide lists flappers at $8 to $20, and CostHelper puts the average part under $25. Five-minute job, no tools.
- Plumber: $60 to $120 according to Fixr, or $50 to $150 or more according to CostHelper. Most of that pays for the visit, not the part.
2. The fill valve won't shut off
A fill valve that never fully closes keeps feeding water into the tank, and the extra spills down the overflow tube into the bowl. The fill valve is the tall assembly, usually on the left side of the tank. It refills the tank after a flush and should click off when the water hits the right level. When it goes bad, usually from sediment or hard-water buildup, it never closes all the way.
Quick test: if the water in your tank sits at or above the top of the overflow tube, the fill valve isn't doing its job. A steady hiss with the lid off points here too.
What it typically costs
- DIY: $15 to $30 for the part. Yelp lists fill valves at $9 to $30, and CostHelper puts the average part under $25. It's a little more involved than a flapper, but still a 20 to 30 minute project for most people.
- Plumber: $60 to $150 for parts and labor according to Fixr, or $50 to $150 or more according to CostHelper.
3. The float is set too high or full of water
The float tells the fill valve when to stop, so a float set too high or a cracked ball float full of water keeps the tank filling. Older toilets have a ball on an arm. Newer ones have a cup that slides up the fill valve shaft. If the float sits too high, the tank fills past the overflow tube. If it's a ball, it can crack and slowly fill with water, and then it never rises high enough to trigger the shutoff.
Quick test: open the tank and look at the water line. It should rest about an inch below the top of the overflow tube. If it's higher than that, the float needs to come down.
What it typically costs
- DIY: often $0, because most modern floats adjust with a clip or a screw. A cracked ball float is a small, inexpensive part. A new float cup comes with a new fill valve, so you pay the fill valve price above.
- Plumber: usually part of the same visit. If the plumber swaps the whole fill valve, expect the fill valve price above.
4. Water is spilling into the overflow tube
Water running into the overflow tube is a symptom, not a broken part: the float or the fill valve upstream is the real problem. The overflow tube is the vertical pipe in the middle of the tank. It's a safety drain, so anything above its rim spills into the bowl instead of onto your bathroom floor.
Quick test: look down into the tank. If a steady stream of water runs into the top of the overflow tube, treat it as a float or fill valve problem, not an overflow tube problem.
What it typically costs
- DIY: $0 for a float adjustment, up to the price of a new fill valve.
- Plumber: the same as the float or fill valve fix it turns out to be.
5. The refill tube is out of place
A refill tube pushed too far into the overflow tube, or clipped on loose, can keep your toilet running. The refill tube is the skinny flexible hose that clips to the top of the overflow tube. After each flush, it sends a small stream of water down to refill the bowl. Pushed too far down, it siphons water out of the tank constantly.
Quick test: make sure the refill tube ends above the rim of the overflow tube, not below it. The little clip that came with the fill valve is meant to hold it in place.
What it typically costs
- DIY: usually $0. Just reposition the clip. A new fill valve also comes with a new refill tube.
- Plumber: usually a quick adjustment during the visit. If the plumber replaces the fill valve, expect the fill valve price above.
What each fix typically costs
Fixing a running toilet yourself typically costs nothing for an adjustment and $5 to $30 for a part, while most of a plumber's bill is the visit. Here's how the five causes compare, using the Yelp, CostHelper and Fixr cost guides cited above:
- Flapper: $5 to $20 to do yourself, or $60 to $120 with a plumber according to Fixr.
- Fill valve: $15 to $30 to do yourself, or $60 to $150 with a plumber according to Fixr.
- Float: often $0 to adjust. A new float cup comes with a new fill valve.
- Overflow tube: a symptom. You pay for the float or fill valve fix behind it.
- Refill tube: usually $0 to reposition.
A plumber's visit usually starts with a service call fee. Yelp puts that fee at $50 to $120, and HomeAdvisor puts it at $100 to $250, usually including the first hour of work. Nights, weekends and emergency calls cost more.
Runhome contractor estimates for a running toilet repair, tank parts and labor, ran from $175 to $395 as of September 2026, including the contractor's trip and assessment, and a full replacement with a new toilet ran from $440 to $1,090.
What moves the price is where you live, whether the call is after hours, and whether the contractor finds a stuck shutoff valve or a hard-to-match part on an older toilet.
When to stop troubleshooting and call a plumber
Call a plumber when new parts don't stop the running, the porcelain is cracked, or the shutoff valve won't close. Most running toilets are a 15-minute fix, but a few situations are worth handing off:
- You've replaced the obvious parts and it's still running.
- You see a hairline crack in the porcelain tank or bowl.
- Multiple toilets in the house are acting up at once, which can point to water pressure or the supply side.
- The shutoff valve behind the toilet is corroded, stuck, or leaking.
- Water weeps from the supply line or the tank bolts, or shows up on the floor.
In those cases, a pro will diagnose it faster than you can swap parts. A handyman can rebuild a tank too, but ask for a plumber when the shutoff valve is stuck, the supply line weeps, or water is on the floor.
A running toilet is cheap to fix and costly to ignore
A running toilet is one of the cheapest, fastest fixes in your house, and one of the most expensive things to ignore. Most of the time you can solve it with a $5 to $20 flapper and a Saturday morning. When you can't, a plumber can rebuild the tank in about an hour, and the toilet stays where it is. Your toilet should be the quietest thing in the house.
Common questions
Why does my toilet refill itself every so often?
A toilet that stays mostly quiet but refills itself every so often is leaking water out of the tank, usually past the flapper. The level drops, and the fill valve does its job by topping the tank back up. A few drops of food coloring in the tank confirm it: color in the bowl without a flush means a flapper leak.
The flapper looks clean and flexible, so why does the toilet still run?
Looks tell you very little, because a flapper seals on a thin ring and a groove you can't see keeps it from closing. Change the flapper first. If dye still reaches the bowl, the seat the flapper lands on is worn, and the flush valve needs replacing.
Why won't my Toto toilet stop running?
A Toto runs for the same reasons as any other toilet, most often a worn flapper or a fill valve that won't shut off. The catch is the part: many Toto models use a 3-inch flapper, wider than the standard 2-inch one, so a mismatched flapper never seals. Match the model number stamped inside the tank or on the lid before you buy a replacement.
It's been running for a long time. Is it still worth fixing?
Yes. A running toilet doesn't settle down on its own, and it keeps sending water down the drain every day you wait. The fix is the same small part it would have been a year ago.
Should I just replace the whole toilet?
Only when the porcelain is cracked or no flapper fits the flush valve anymore, which happens on some toilets more than 15 years old. Otherwise, a tank rebuild costs a fraction of a replacement, and the toilet you have is usually fine. See the full guide to a running toilet for when each part is worth changing.