How to Fix a Running Toilet

Mark the Water Level

To test if your flapper is leaking, start by flushing the toilet. When it is done refilling, mark the water level of your tank with a pencil.

Turn off the Water Supply Line

Turn off your water supply line. Wait for a minimum of 25 minutes. If your water level drops below the pencil mark, you have a leak in your toilet tank.

Wait for a Few hours

Leave the water off for a couple of hours and see where the water level drops. If the water level drops to the flapper or seal, you need to replace it. If the water level drops to a point on your overflow tube or the bottom of the tank below the flapper, you need to replace your flush valve and tank-to-bowl gasket.

Like toilet flappers, most fill valves use rubber seals that can wear down over time from repeated use. If your flapper is sealing properly but your toilet is still running, it may need to be serviced or replaced.

Start by flushing the toilet and watching the tank refill. If water continues flowing after the tank is full or if the float does not rise and shut the valve off, the fill valve is not functioning correctly. If you have a Korky fill valve, you can service it.

If a replacement is needed, refer to our guide on how to change a fill valve for step-by-step instructions.

If you recently installed a new flapper or seal and your toilet is still running, the issue is often related to fit or adjustment rather than the part itself.

Confirm You Have the Right Flapper or Seal

If your toilet uses a flapper, make sure it matches the size of your flush valve opening. Tower-style or canister flush valves typically require a specific replacement seal designed for that model. If you're unsure which seal you need, refer to our guide on identifying your flush valve and selecting the right seal.

Check the Flapper Chain Length

If you have the correct size flapper, make sure the chain is not too tight or too loose. We recommend only leaving 1-2 chain links in slack so it doesn't get in the way or hold the flapper open when you flush the toilet.

Check the Flush Valve

Inspect the flush valve for debris buildup, mineral deposits, or visible damage that could prevent a proper seal and cause leaks. If you notice cracks, warping, or other damage, you need to replace the flush valve.