Fixing a Running Toilet

9 min readFeb 17, 2026

A running toilet is one of those little household annoyances that somehow manages to feel both harmless and maddening at the same time. You hear that soft trickle, then a hiss, and it flushes itself as if there were an invisible hand pressing the handle.

When I was a kid, my dad who is not mechanically inclined decided to fix our bathroom toilet. It seemed to take hours with several trips back and forth to the hardware store. Years later as an adult I was confronted with a running toilet. Remembering that fateful day years prior, I dreaded the thought of having to fix it. A plumber was going to be too expensive so I decided that I would set aside a weekend and fix it myself.

I went to the hardware store and spoke to one of their plumbing experts . Not knowing specifically what was wrong, he set me up with a full toile tank replacement parts kit as well as a few tools that would make things a bit easier.

Returning home I dived into it, so to speak. Less than an hour later I had replaced the most likely parts and the toilet was working properly. I’m not sure why it was so troublesome for my dad, but I came to the realization that things may not be as difficult as I remember them.

I believe that with a bit of explanation, this is one of the simpler household DIY tasks that most homeowners can do on their own.

The basic plan is to:

Get familiar with what’s inside the tank
Figure out the root cause of the problem
Gather the parts and tools necessary to fix the problem
Fix the problem and call it a day
What to do if you still have a problem

Standard Disclaimer — READ ME

Step 1: Get familiar with what’s inside the tank

If you’ve never opened a toilet tank before, it can feel like you’re about to peer into some mysterious plumbing abyss. But once you lift the lid, you’ll see it’s basically three main parts doing all the work:

The flapper — the rubber piece at the bottom that lifts when you flush and seals when the tank refills.
The fill valve — the tall assembly that lets water into the tank.
The float — the part that tells the fill valve when to stop filling.

Here is a typical view of the parts inside the tank:

In some cases the ‘ball’ float is part of the fill / float valve. For example:

A toilet “runs” when one of these pieces isn’t doing its job. Usually it’s either the flapper not sealing, the float letting the water rise too high, or the fill valve refusing to shut off.

Step 2: Figure out the root cause of the problem

Many people don’t realize that the water in the tank is clean. It’s the same water that comes out of your sink faucet. So while it’s not glamorous, it’s not gross either.

Start by turning off the water to the toilet first. This valve is usually on the left side of the toilet at the wall. Turn it clockwise until it stops. The water should now be shut off.

Flush to empty the tank.

If the tank starts to fill, you have either not turned the valve to full closed, or the valve is broken. Turn the valve counter-clockwise to open it, and then try turning it clockwise again to see if it was just sticking. Do not force it as you do not want to break it. If you cannot get the valve to shut off, you may actually need to hire a plumber.

Once the water is shut off and the tank is mostly drained, you’re ready to diagnose.

Turn the water back on for a moment and watch what happens inside the tank.

Is the water trickling into the bowl? That’s almost always a flapper issue.
Is the water rising too high and spilling into the overflow tube? The float is set too high.
Is there a constant hissing near the fill valve? The valve may be worn out.

The Flapper

To test the flapper, try jiggling the handle. If this stops the running temporarily, the flapper or chain is involved.

I remember when I once helped a neighbor who was convinced his toilet needed a full parts replacement. It turned out that the chain was so long it kept slipping under the flapper and holding it open just enough to leak. The frustrating part for him was that this did not happen every time, and it took us a while to actually see it happen. We shortened the chain by one link and the toilet behaved like it had been scolded.

A similar situation was due to a plastic chain. The chain would actually float on the water, and being too long it would sometimes get caught on the overflow tube and prevent the flapper from closing.

The Overflow Tube

The overflow tube prevents the water from overflowing the tank and flooding your bathroom. If the float is set too high, the water will either never turn off or, it may be set just high enough that the water turns off but then it drains just a bit and it drains a bit more causing the fill valve to open briefly.

The fix will depend on which type of float you have.

If its a ball float on a metal rod, then the solution is to CAREFULLY bend the metal rod down so that the ball doesn’t have to rise as high to turn off the valve.

If its a cylindrical float that rides along the fill valve, then there is usually an adjustable arm that can be turned to raise or lower the float to change the water level in the tank.

A rule of thumb that I use is that the water level should be no higher than an inch below the mouth of the overflow tube.

The Fill Valve

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If the fill valve is the cause, it cannot be fixed, it must be replaced.

Step 3: Gather the Parts and Tools Necessary to Fix the Problem

There are only a handful of simple tools that will will need for most toilet fixes. These include:

An adjustable wrench or pliers (also known as channel locks)
Pliers
A towel or sponge
A small bucket
A replacement flapper or fill valve (depending on what you have identified as the root cause of the problem

Step 4: Fixing the Problem

The Flapper (the most common culprit)

If you see water slowly moving from the tank into the bowl, start here. Flappers wear out, warp, or get coated in mineral buildup over time.

Remove the old flapper

Turn off the water.
Flush to lower the water level.
Unhook the chain from the handle arm.
Unclip the flapper from the pegs on the overflow tube.

Install the new flapper

Clip the new flapper onto the same pegs on the voerflow tube.
Reattach the chain.
Adjust the chain so there’s just a little slack — too tight or too loose both cause problems.

Test The Fix

Turn the water back on and let the tank fill. If the running stops, you’re done. If not, move on to the float.

The Float

If the water level rises too high, it spills into the overflow tube and the toilet never stops running. You need to adjust the float.

Identify your float type

You’ll see one of these:

Float cup — a plastic collar that slides up and down the fill valve.
Float ball — the old‑school ball on a metal rod.

Adjust a float cup

Look for a screw on top of the fill valve or a clip on the float.
Turn the screw or slide the clip to lower the float.
Aim for the water to stop about an inch below the top of the overflow tube.

Adjust a float ball

Gently bend the rod downward so the ball sits lower.

I once saw a toilet where the water level was so high it was practically at the rim of the tank. The homeowner thought it made the flush “more powerful.” In reality, the overflow tube was acting like a permanent drain. A 30‑second float adjustment fixed everything.

If adjusting the float doesn’t help, the fill valve may be the issue.

The Fill Valve

If you hear constant hissing or the water never fully shuts off, the fill valve may need replacing. It sounds like a big job, but modern kits are designed for DIYers.

Remove the old valve

Turn off the water.
Flush and soak up remaining water. If you don’t then the remaining water will drain from the tank when you unscrew the fill valve.
Disconnect the water supply line from the fill valve under the tank. In the photo above that shows the water shutoff valve you will see a white plastic nut that connects at the bottom of the tank. (Note: This may be a different color and it may also be made of metal depending on the make, model, brand, etc.) Unscrew the white plastic nut that is holding the fill valve in place.
Lift the old valve out.
Cleanup any water that may have drained from the tank.

Install the new valve

BEFORE you insert it into the tank, adjust the height according to the instructions. Its much easier to do before you put it into the tank.
Insert it into the tank.
Screw on and tighten the mounting nut underneath to reconnect the water supply line to the fill valve.
Attach the refill tube to the overflow tube.

Test and adjust

Turn the water back on and adjust the float so the water stops at the right level.

Step 7: What to do if you still have a problem

If you’ve replaced the flapper and fill valve and the toilet still leaks into the bowl, the flush valve seat (the surface the flapper seals against) may be damaged. Fixing that requires removing the tank from the bowl and installing a new flush valve assembly.

It’s doable, but it’s a bigger project. This requires that you remove the tank from the bowl in order to be able to remove the overflow valve and flapper assembly. To do this you need to remove the bolts holding the tank to the bowl. You then need to gently lift and separate the tank from the bowl and gently place it upside down on some towels on the floor. Bear in mind that the tank is HEAVY and awkward and possibly slippery.

There are more steps involved, but if you’re not comfortable with this level of disassembly so far, this is the point where you may want to call a plumber.

A Partial Fix

If the toilet is still draining and you’ve done everything short of dismantling the tank to change the overflow assembly, there is something you can do that doesn’t fix the root cause, but makes it a bit more livable short of having to hire a plumber.

Fluidmaster has a product that they call the ‘Leak Sentry’. This is a fill valve with an extra device that prevents the automatic refill of the toilet by preventing the fill valve from opening until you actually flush the toilet. While it doesn’t stop the toilet from draining, it eliminates the constant drain / fill cycle.