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How to Stop a Toilet Fill Valve from Leaking: Step-by-Step Guide

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If you have a leaking toilet fill valve you may notice a puddle of water around your tank. This is a common problem and fortunately not difficult to fix. The toilet fill valve is responsible for regulating how much water is in the tank, so it's a good idea to learn how it works and how to fix it when something goes wrong.

It's possible you'll be able to fix the issue with a little elbow grease or an adjustable wrench, but you may need to replace the toilet fill valve itself. Don't worry, none of the repairs are difficult and you should be able to do them yourself with out the need of calling a plumber.


R&T A1250L Toilet Fill Valve Toilet Tank Parts Replacement Running Toilet Repair Kit Quiet Fill Anti-Siphon

Click on the photo above to learn more about the R&T Fill valve.

What is a Toilet Fill Valve?

The fill valve in a toilet is also sometimes called the ballcock. It's responsible for regulating how much water comes into the tank when the toilet is flushed.

When the toilet is flushed, the fill valve will stay "open" until the tank has filled to the appropriate level.

There's a variety of styles of fill valves available, so if you need to replace yours, you'll want to make sure you purchase the appropriate one for your toilet.

Learn How a Fill Valve Works


Fluidmaster 400H-002 Performax Universal Toilet Fill Valve High Performance Tank and Bowl Water Control, 1-Pack, Multicolor

Click on the photo above to learn more about the FluidMaster Fill Valve.

How to Fix a Leaking Toilet Fill Valve

If you suspect your toilet fill valve is leaking, you've probably noticed a few droplets of water or even a puddle under your toilet tank. 

There are a number of things that can cause a toilet fill valve to leak. Here are the most common:

Loose Locking Nut

The locking nut's job is to keep the fill valve tight and secured to the rest of the toilet. The locking nut is located below the toilet tank, and over time it can loosen and water may begin to leak.

Sometimes the seal to the fill valve will breakdown and need to be replaced. This can be checked when you tighten the locking nut.

The most obvious signs of a loose locking nut is a puddle of water below the toilet tank. 

The Fix

  • Turn off the water supply to the toilet.
  • Check the seal between the fill valve and the bottom of the tank. Replace if needed.
  • Tighten the locking nut with a wrench (in order to get a snug fit, hold onto the fill valve within the tank).
  • If you're unable to tighten the locking nut, you'll need to replace it with a new one.

Damaged Fill Valve

The most common reason a toilet fill valve leaks is due to wear and tear. Over time, these parts simply wear out and need to be replaced.

It's also possible the fill valve was damaged if you needed to remove it in order to work on your toilet. Most fill valves are made of plastic so they can break if dropped or over tightened when installed.

The Fix

If your fill valve isn't working properly, and you suspect it was damaged, the best thing to do is to replace it with a new one. Fortunately, they are inexpensive (usually under $20) and relatively easy to install yourself.

Mineral Deposits

Water contains minerals and overtime the minerals can buildup on the surfaces they come in contact with. This is especially a concern if you live in an area with hard water. 

Occasionally the toilet fill valve will develop a mineral buildup which may cause it to start leaking, or may even buildup within the moving parts and not allow it to function properly.

The Fix

You have two choices when this happens, you can try to clean the fill valve or simply replace it with a new one. 

If your fill valve is older, you may want to upgrade it. Once you go through the hassle of trying to clean it, it's just as easy to buy a new one.

However, if you do want to clean it up, here's how:

  • Turn off the water supply and flush the toilet.
  • Add 3 parts water to 1 part vinegar to a spray bottle.
  • Using a sharp knife or razor blade, remove any old sealant from the base of the fill valve.
  • Spray the vinegar/water solution to the area and gently wipe with a clean cotton cloth.
  • Mix baking soda and water and apply using a cotton ball to mineral deposits on the exterior of the fill valve.
  • After 15 minutes, rinse the baking soda and water from the fill valve.
  • Using a Q-tip or small brush, clean the access ports and valves on the fill valve.
  • Rinse and turn the water back on.
Korky 528 Toilet Fill Valve, Universal, Black

Click on the photo above to learn more about the Korky Fill Valve.

How to Replace a Toilet Fill Valve

If you've determined that you need a new toilet fill valve, then you'll want to make sure you purchase one that's compatible for your toilet.

Here's a video that explains some of the different toilet fill valves:


Step-by-Step Directions on How to Replace a Fill Valve

toilet water shut off

Step One - Empty the Tank

  • Turn off the water supply and disconnect the supply line to the toilet.
  • Flush the toilet to empty the tank.
  • Remove the tank cover and float ball (if your toilet uses one)
  • Use a sponge to collect any excess water in the tank.

Loosening the Lock Nut on the Toilet Fill Valve

Step Two - Remove the Fill Valve

  • Remove the locking nut to the fill valve with an adjustable wrench (located below the tank).
  • With the locking nut removed, you'll be able to reach into the tank and pull out the fill valve.

New Toilet Fill Valve Ready to Be Installed

Step Three - Prep the New Fill Valve

  • Adjust your new fill valve so the marking on top of the fill valve is at least 1-inch above the overflow tube.
  • Be sure to follow the instructions for your new fill valve as they may differ.

Attaching Locking Nut to New Toilet Fill Valve

Step Four - Install the New Fill Valve

  • Place the new fill valve into the tank so the shank protrudes through the hole at the bottom of the tank.
  • Install the locking nut to the fill valve's shank and press the fill valve down while tightening to ensure a snug fit. 

Attaching the fill line to the fill tube

Step Five - Fill the Tank

  • Attach the refill tube to the overflow tube (trim the tube if necessary).
  • Connect the water supply line to the toilet and turn on the water.
  • While the tank is filling, check the water level and adjust the fill valve's height if needed. 
  • Check for leaks and tighten connections if necessary.

Watch the Video

Last update on 2024-04-16 / Affiliate links / Images from Amazon Product Advertising API

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