How to Fix a Running Toilet in 15 Minutes

Home Maintenance6 min readJune 1, 2026

If your toilet won’t stop running, you’re not just annoyed — you’re paying for it. A constantly running toilet can waste hundreds of gallons of water a day. The good news: nine times out of ten, it’s a five-dollar part and fifteen minutes of your time.

Step 1: Figure out what’s actually running

Lift the tank lid and watch the water. There are three usual suspects:

The flapper isn’t sealing the flush valve at the bottom of the tank.
The fill valve keeps refilling past the fill line.
The float is set too high, so water spills into the overflow tube.

Step 2: Check the flapper first

Flush the toilet and watch the flapper drop back into place. If it doesn’t seal flat, or if it looks warped, cracked, or coated in mineral buildup, that’s your problem. Flappers are cheap and universal — replacing one takes about five minutes with no tools required.

Turn off the water supply valve behind the toilet.
Flush to drain the tank, then unhook the old flapper from its pegs.
Disconnect the chain from the flush lever.
Attach the new flapper, reconnect the chain, and turn the water back on.

Step 3: Adjust the float if the flapper isn’t it

If water is trickling into the overflow tube, lower the float (either the ball or the cup-style float, depending on your fill valve) until the water level sits about an inch below the top of the overflow tube.

Step 4: Replace the fill valve if it’s still running

If neither fix stops the sound, the fill valve itself may be worn out. Fill valve kits are inexpensive and install in about the same steps as a flapper — shut off the water, drain the tank, unscrew the old valve, and thread in the new one.

When to call a plumber

If you’ve replaced the flapper and fill valve and it’s still running, or if you notice water pooling around the base of the toilet, that’s beyond a weekend fix — get a plumber out before it turns into a bigger repair (or a conversation with your landlord about water damage).