How to Fix a Running Toilet
A running toilet wastes water and drives up your bill, but it's almost always one of three simple parts. Here's how to find out which — and fix it yourself in about 15 minutes.
If your toilet keeps running — or you hear it randomly kick on for a few seconds every so often — the tank isn't sealing water correctly. Take the lid off the tank and flush it while watching what happens inside. It's almost always one of these three parts.
1. Check the Flapper
The flapper is the rubber piece at the bottom of the tank that lifts when you flush and drops back to seal the tank. Over time it warps, cracks, or collects mineral buildup and stops sealing fully — this is the most common cause of a running toilet by far.
Fix: If it looks worn, warped, or doesn't sit flat when closed, replace it. Flappers are inexpensive and sold at any hardware store — just match the size to your existing one.
2. Check the Float Height
The float rises with the water and shuts off the fill valve once the tank is full. If it's set too high, water keeps flowing into the overflow tube in the center of the tank, and you'll hear a faint, constant trickle.
Fix: Adjust the float (either a screw or a clip, depending on your toilet's age) so the water level sits about an inch below the top of the overflow tube.
3. Check the Fill Valve
If the flapper and float both look fine but you still hear hissing or the tank won't fully stop filling, the fill valve itself may be worn out.
Fix: Fill valves are a slightly more involved replacement (you'll need to shut off the water supply to the toilet first) but are still a reasonable DIY job with a wrench and about 20 minutes.
When to Call a Pro Instead
If you've replaced the flapper and adjusted the float and it's still running, or if the shutoff valve under the toilet is stuck, corroded, or won't turn — stop there. A stuck shutoff valve can turn a simple fix into a real leak fast, and that's worth a professional's five minutes rather than a DIY afternoon.
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