Plumbing guide
Toilet keeps running: find the cause and fix it
By the Home Doctor team · Reviewed
Quick answer
A toilet that keeps running almost always has one of three problems inside the tank: a worn flapper that lets water leak into the bowl, a fill valve set too high so water spills into the overflow tube, or a lift chain that's too short or tangled. All three are DIY fixes with parts under $30 and 15 to 30 minutes of work. The EPA estimates a leaking toilet can waste about 200 gallons of water a day.
- How urgent
- Fix soon
Not dangerous, but it wastes water and raises your bill every day it runs.
- DIY or pro
- DIY
No special tools. Shut off the valve behind the toilet, and bring the old part to the store to match it.
Common causes and how to tell them apart
1. Worn or warped flapper
- How to tell
- The tank refills by itself every so often. Or add a few drops of food coloring to the tank: if color shows up in the bowl within 15 minutes without flushing, the flapper leaks.
- What fixes it
- Replace the flapper. Match the size (2 or 3 inch) and the brand if you can.
2. Fill valve set too high
- How to tell
- The water level rises above the top of the overflow tube and trickles into it.
- What fixes it
- Lower the float so the water stops about 1 inch below the top of the overflow tube, or at the fill line.
3. Chain too short or tangled
- How to tell
- The flapper doesn't sit flat after a flush.
- What fixes it
- Adjust the chain so there's about half an inch of slack.
4. Failing fill valve
- How to tell
- Constant hissing, or the water won't shut off even when you lift the float by hand.
- What fixes it
- Replace the fill valve.
5. Cracked overflow tube or flush valve
- How to tell
- Water keeps draining even with a new flapper and the level set correctly.
- What fixes it
- Replace the flush valve. It's a bigger job because the tank comes off the bowl.
Not sure which one you have?
Snap a photo. Home Doctor narrows it down, tells you how urgent it is, and prices the fix.
Diagnose it from a photoFirst diagnosis free. No account needed.
What you can safely try first
- 1Take the tank lid off and watch one full flush and refill.
- 2Lift the float by hand. If the running stops, lower the float.
- 3Do the food-coloring test for the flapper.
- 4Check the chain slack.
When to call a pro
- Water on the floor around the base (wax ring, or a cracked tank or bowl).
- The shutoff valve behind the toilet won't close or leaks itself.
- New parts don't fix it.
What it costs
| Job | DIY parts | Pro, installed |
|---|---|---|
| Replace flapper | $5–$15 | $100–$200 |
| Replace fill valve | $10–$25 | $125–$250 |
| Replace flush valve | $15–$40 | $175–$350 |
| Replace the toilet (standard model) | $150–$400 | $400–$1,000 |
Ballpark US ranges as of September 27, 2026. Your region, access and the specifics of your home can move these a lot. Get two or three quotes for anything over a few hundred dollars.
What to tell the pro
My toilet keeps running. I've [replaced the flapper / adjusted the float / checked the chain] and it still [refills every few minutes / hisses constantly / drains into the overflow]. The shutoff valve [works / is stuck]. There [is / isn't] water on the floor at the base.
Questions people ask
How much water does a running toilet waste?
A lot. The EPA estimates a leaking toilet can waste about 200 gallons a day, which shows up on your water bill fast.
Is a running toilet an emergency?
No. If you can't fix it right away, turn off the shutoff valve behind the toilet between uses.
Why does my toilet run for a few seconds on its own?
That's a phantom flush: water slowly leaks past the flapper until the fill valve tops the tank back up. A new flapper almost always fixes it.
Get an answer for your house
Every house is different. A photo gets you the likely cause, how urgent it is, and a fair price, in about 30 seconds.
Diagnose it from a photoFirst diagnosis free. No account needed.
General guidance, not a substitute for a licensed professional who can see the problem in person. If you smell gas, see sparks or smoke, or anyone is hurt, leave the area and call 911.