How to Fix a Running Toilet

Is your toilet constantly running? This common toilet problem can have a large impact on your water bill. If your toilet is running intermittently, there are a couple of potential issues your toilet may have.


The first, and most common, is a leaky flapper. Different parts of the country deal with different types of water. From harsh municipality water to well water, all wreak havoc on the life of a toilet flapper. The most common, and quickest fix is to replace your leaking toilet flapper.


The second common cause your toilet keeps running is a malfunctioning or improperly installed fill valve. If your fill valve has an external float, the build-up can cause the float to stick and prevent it from working.

Does this describe your toilet issue?

Why Do Toilet Flappers Leak?

More times than not, your flapper is the cause of your running toilet. As the flapper slowly leaks, it causes the fill valve to do its job, so you hear your fill valve running.


Flappers can leak for a few reasons, the most common being age. Flappers typically have a life of 4-5 years. Chemical cleaning tablets and mineral deposits from hard water can sometimes make the flapper wear out faster.


Another reason your flapper could leak is that the flapper chain length is wrong. If the chain has too much slack, it could get hung up when you flush the toilet. If the chain is too tight, the flapper will remain partially open, which causes the water in the tank to drain.


If you bought a new flapper and your toilet is still running, confirm you have the right size flapper. If you have a large 3-inch flush valve opening but installed a standard 2-inch flapper, the flapper will not seal correctly.


How to Test the Flapper


Test if your flapper is leaking by marking the water level of your tank with a pencil.

Mark waterline with pencil

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

Turn off Water Supply

Leave the water off for a couple of hours and see where the water level drops. If the water level drops to the flapper, you need to replace your flapper

Leaking toilet flapper

If the water level drops to the bottom of the tank, you need to replace your flush valve and tank-to bowl gasket.

Why Do Fill Valves Cause a Running Toilet?

Fill valves are responsible for refilling the tank and the toilet bowl through the top of the overflow tube. Although causing a running toilet is less common, it can sometimes malfunction.

Normal wear and tear occurs with the repeated cycling of a fill valve. The rubber seals located inside the valve degrade over time. The type of water you have is a factor in how long your fill valve will last. Well-water and treated water have different additives that affect this.

Treated water often includes different chemicals that may or may not cause the rubber seals in your fill valve to shrink or warp. To combat this, the 2X Long Life Fill Valve is the longest-lasting universal valve with a 10-year warranty.

Over time, your fill valve will clog with calcium deposits. This normal aging process takes place over a few years and can cause your fill valve to lose efficiency over time. Korky models are serviceable, enabling our customers to combat this without removing the tank.

If your tank is not leaking but your toilet is still running, you may need to service or replace the fill valve. To confirm this, you will need to test your fill valve.

How to Test the Fill Valve

Testing the fill valve is easy. When your toilet flushes, observe the water refilling the tank. If the water keeps running, or the float fails to rise properly, you should replace the broken fill valve.

Adjusting the float is sometimes a solution to water leaking through the flush valve overflow tube, which will cause a running toilet. Korky valves feature internal floats, so lowering the height will accomplish this.

If you get a new Korky fill valve, read our guide about how to change a fill valve to learn more about installation.

How to fix a running toilet