Toilet Keeps Running? 7 Fixes That Stop It Fast

1. Confirm where the water is going

Take the lid off the tank and look inside while the toilet is running. If water is flowing into the overflow tube (the tall open pipe in the middle), the water level is set too high. If water is seeping from the tank into the bowl without the overflow tube running, the flapper is leaking.

Knowing which one it is saves time. An overflow problem points to the float or fill valve. A slow leak into the bowl points to the flapper or the chain. Both are easy fixes that need no special tools.

2. Replace a worn-out flapper

The flapper is the rubber seal at the bottom of the tank that lifts when you flush and drops back down to seal the tank. Over time, chlorine and minerals make it warp, crack or get slimy, so it no longer seals and water leaks into the bowl nonstop.

Replacing it is a five-minute job and the part costs under ten dollars at any hardware store. Here is how to do it:

1. Turn off the water supply valve behind the toilet and flush to empty the tank.
2. Unhook the old flapper from the pegs on the overflow tube and detach the chain.
3. Take the old flapper to the store so you can match the size (2-inch and 3-inch are the common ones).
4. Hook the new flapper onto the pegs, reconnect the chain with about half an inch of slack, and turn the water back on.

3. Adjust the float to lower the water level

If water is running into the overflow tube, the float is letting the tank fill too high. On older toilets the float is a ball on a metal arm: gently bend the arm down so the ball sits lower. On newer toilets the float is a cup that slides on the fill valve shaft: squeeze the clip on the side of the cup and slide it down about an inch.

The correct water level is about one inch below the top of the overflow tube. Flush and let the tank refill, then check. Lower the float a little more if water still reaches the overflow tube.

4. Fix the chain length

The chain connects the flush handle to the flapper. If it is too short, it holds the flapper slightly open and water leaks constantly. If it is too long, it can get caught under the flapper and prevent a seal, or tangle so the flapper cannot drop.

Adjust the chain so there is about half an inch of slack when the flapper is closed. Unhook it from the handle arm and move it one or two links in either direction until the flapper drops freely and seals flat.

5. Clean or replace the fill valve

The fill valve (also called the ballcock) refills the tank after each flush. If it is clogged with sediment or its seals are worn, it may never shut off fully and you will hear a constant hissing or trickling sound.

First try cleaning it: turn off the water, remove the cap on top of the valve, and rinse out any grit under the seal. If the hissing continues, replace the whole valve. A universal fill valve costs about fifteen dollars and installs with one adjustable wrench in under 20 minutes.

6. Try the food coloring test

If you are not sure whether the flapper is leaking, add a few drops of dark food coloring to the tank water and wait 15 minutes without flushing. If color appears in the bowl, water is leaking past the flapper and it needs to be replaced.

This test is also useful after a repair to confirm the fix worked. Clear bowl water after 15 minutes means the seal is holding.

7. Check the overflow tube height

On rare occasions the overflow tube itself is the problem, usually after a cheap replacement fill valve was installed that sits too tall. If the tube is cut too short or the valve is too tall, the tank can never fill to the right level and water runs constantly.

Compare the water line mark inside the tank (usually stamped on the back wall) with the top of the overflow tube. The tube should extend at least an inch above the marked water line. If it does not, the fill valve assembly needs to be adjusted or replaced.

When to call a licensed plumber

Call a professional if you have replaced the flapper and fill valve and the toilet still runs, if you see water leaking from the base of the toilet onto the floor, or if the tank itself is cracked. A leak at the base usually means a failed wax ring, which requires removing the toilet. Persistent running after new parts can also signal a hairline crack in the overflow tube or a corroded flush valve seat, both of which are easier for a licensed plumber to fix correctly the first time.