How to Fix a Running Toilet
A running toilet can waste 200 gallons of water per day — adding $50–$100 to your monthly water bill. Most running toilets are caused by one of three cheap, easy-to-replace parts: the flapper, fill valve, or float. This is one of the most rewarding DIY repairs you can do.
Likely Causes
- 1Worn or warped flapper not sealing the flush valve
- 2Flapper chain too long or caught under the flapper
- 3Fill valve set too high — water overflows into overflow tube
- 4Defective fill valve that doesn't shut off
- 5Float set too high or waterlogged (older ball-float designs)
Wastes 200+ gallons per day. Should be fixed within a week to avoid significant water bills.
How to Fix It: Step by Step
- 1Diagnose the problem
Remove the tank lid. Add a few drops of food coloring to the tank. If color appears in the bowl without flushing, your flapper is leaking.
- 2Check the flapper chain
The chain should have 1/2 inch of slack. Too short prevents the flapper from seating; too long can get caught under the flapper.
- 3Inspect the flapper
Feel the flapper. If it's rigid, warped, or has visible mineral buildup, replace it. Flappers cost $5–$10 and take 10 minutes to swap.
- 4Check the fill valve and float level
The water level in the tank should be 1 inch below the top of the overflow tube. If water is running into the overflow tube, lower the float or adjust the fill valve.
- 5Replace the fill valve if needed
If adjusting doesn't stop the running, replace the fill valve. A Fluidmaster 400A is the universal standard and costs $12–$15.
- 6Test the repair
Flush the toilet and observe. The tank should fill completely and the fill valve should shut off cleanly.
Materials & Tools Needed
Warning Signs It's Getting Worse
- ⚠Toilet starts making gurgling sounds
- ⚠Water appears on the floor around the toilet base
- ⚠Toilet doesn't flush completely
When to Call a Professional
Call a plumber if the toilet rocks or is loose at the floor (wax ring issue), if the tank is cracked, or if the toilet continues running after replacing the fill valve and flapper.
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