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How to fix a running toilet

Here's how to troubleshoot and fix a running toilet yourself, without calling a plumber.

Brian Bennett Former Senior writer
Brian Bennett is a former senior writer for the home and outdoor section at CNET.
Brian Bennett
4 min read

Does your toilet run all the time or at odd moments? Here's how to troubleshoot the problem.

Brian Bennett/CNET

Sometimes toilets act up. One common problem your trusty throne can develop is that it always runs. This constant flow of water is a noisy nuisance -- and it's also a money-waster that you'll end up paying for on your next utility bill.

Fortunately, it's usually a pretty easy problem to fix. In this guide, I'll lay out the likeliest causes for continually running toilets, and I'll also explain the first steps you should take to troubleshoot and solve the problem. Once you've successfully dealt with it, you'll not only save some cash, but you'll have gained the skills to tackle running toilets whenever and wherever you encounter them.


Always turn off the water before working on your toilet.

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Step 1: Turn off the water

The first step is to turn off your toilet's water supply. Usually it's a small knob on the wall to the right of the toilet that sits close to the floor. Turn the knob all the way to the right (clockwise) to close the valve and pinch off the water supply. Doing the opposite turns the water back on.


Remove the water tank lid to see what's happening inside.

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Step 2: Remove the tank lid

Carefully remove the ceramic lid from the top of the water tank. It's fragile, so be sure to lower it gently onto a safe resting spot like a bath towel. Now, take a look around. Inside the tank you should see all the main parts responsible for your toilet's water control. These are the flush valve, the fill valve, and the fill tube.


Here's a look at a toilet's water control system. On the left is the fill valve. On the right is the fill tube, flapper, and flush valve.

Brian Bennett/CNET

The fill tube is a hollow plastic cylinder mounted vertically to the floor of the tank. One end of the tube is positioned above the tank's water line. At the other end of the fill tube in the bottom of the tank is the flapper, the rubber or silicone seal around the drain that lifts every time you flush.

The purpose of the fill tube is to accept water from the fill valve to refill the water tank after each toilet flush. It also serves as an overflow pipe to keep water from overflowing the tank. 

As the water level in the tank lowers, so too does the float in the fill valve. A lowered float opens the fill valve and lets water refill the tank. Then, as the float rises again, the water stops running once it reaches a preset level.

Step 3: Check the flapper

Sometimes a constantly running toilet is caused by a faulty flapper. If it isn't sealing correctly in between uses, the water will gradually drain from the bottom of the tank, and the toilet will run endlessly in a futile bid to fill it back up.

To check if this is the case, press your finger around the flapper's edges. If the toilet stops running, then your flapper has a bad seal. Next, document how the flapper connects to the bottom of your toilet. Take pictures so you have a record handy, and note the make and model of your toilet, as these details will help you to track down a matching replacement part.


Take the cap off of the toilet fill valve.

Brian Bennett/CNET

Step 4: Examine the fill valve

Fill valves can fail over time too. Dirt, debris, or mineral scale deposits can cause the valve to open randomly, making the toilet run intermittently. One quick fix for this problem is to purge the valve. My toilet's fill valve is a Fluidmaster cup-style model. To flush it first reach into the tank with your right hand.

Next lift the float up with it resting on top of your hand. Now grip the valve cap with your left hand and rest your thumb across the cap arm. The arm juts out sideways from the valve cap. Press down on the cap while twisting it counterclockwise one-eighth of a turn. Pulling up should then release the cap. 


A quick method that might fix your toilet is to flush the fill valve.

Brian Bennett/CNET

Place a cup upside down on top of the valve. Turn the water supply back on to full force. Water will then flow through the valve, clearing any debris. Do this for 10 to 15 seconds, then shut off the water. Reverse the earlier steps to reattach the valve cap. This may solve your running toilet issue. It did in my case.

Another fill valve problem is if the float is set too high. That means the water level in the tank sits above the fill tube. This causes water to constantly drain into the fill tube. It can also lead to water spilling onto the bathroom floor if the toilet ever clogs.

Adjust the water level by first removing the valve cap as before. Next, remove the refill hose from its nipple on the valve shaft. Now, turn the valve shaft clockwise to lower the water level. Turning the valve shaft counterclockwise will raise the water level. 

Step 5: Swap in a replacement fill valve if necessary 

It may be the case that no amount of cleaning or fiddling will fix your toilet. For example, your fill valve may have failed completely. Your only recourse then is to swap it out for a new unit. It's certainly a more involved process than the other steps above. That said, doing so will greatly increase the lifespan of your toilet. And if your toilet is very old, it'll likely make its water consumption a lot more efficient.