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How to Fix a Leaking Toilet Fill Valve in 3 Steps

How to Fix a Leaking Toilet Fill Valve in 3 Steps

Replacing or fixing a leaking toilet fill valve can seem like a daunting task. Many years ago as a kid I remember helping my dad troubleshoot ours, and I recall being worried we’d do something wrong once we started fiddling with parts.

After fixing fill valves multiple times over my life I can assure you:

There’s nothing complicated about this issue, and I’ll be laying out simple solutions for you to make use of. 

With my instructions, you’ll understand a bit more about how things work when it comes to toilet tank issues.

Within no time, you’ll be able to fix your issue and get your toilet running the way it should be. 

Okay, let’s get to it. It’s time to look at why water is leaking out of the fill valve in the toilet when you flush. 


At first glance:

It may appear as if the issue is your toilet fill valve. However, it could just be that your bottom washer below the valve has deteriorated, and it’s causing a leak.

The way to know whether this is happening is to see if water is coming out of the back of the toilet. If not, that isn’t the cause.


It could also be your float valve. This detects the changes in elevation of water and shuts the water on or off accordingly.

This can stop up due to a calcium build-up.

old float valve needs cleaning

Speaking of float valves:

You might be wondering how to repair a float cup valve in a toilet. We’ll get to that in the next section. 

That said, most likely, you’ll have to know how to replace a fill valve. Or, you might only need to know how to fix it.

As I’ve already mentioned, you either have to replace the entire mechanism, or you might be able to get away with simply replacing a seal inside the unit itself. 

If it’s the latter, you’ll have to get a seal that fits your specific model. If you happen to own a Fluidmaster 400A, you can easily buy a new seal.

Another potential issue is the flush valve gasket, which might be leaking. This’ll require a replacement. 

Let’s Begin

For starters, it’d help to understand how the toilet tank works. 

Whether you have a Kohler, Toto or Cadet brand toilet, it was designed to hold the water that’s ready to go into your toilet bowl once you flush it.

When you flush, the water pours down a drain opening in the center blocked by a rubber flapper and fills the toilet bowl. This tank consists of two different types: the fill and the flush valve.

In either case, these parts simply open and close to let water go down in one direction. 

In this way, they are not a check valve since water can’t return back up the way it came given the design.

There are four different variations; two are older, and two are commonly found on newer toilet models. 

They’re the float cup and floatless fill variety (these are the newer types). The older types are the diaphragm-type ballcock and the plunger-type ballcock. 

Replacing the Valve Seal

washers and hardware for leaking tank valve

Buy this hardware here

I mentioned this earlier. It’s always good to check the valve seal. 

It’s not uncommon for a toilet fill valve to be leaking. 

This method applies only to the newer styles, namely the float cup and the floatless fill valves. 

What you’ll need:

  • A new fill valve fitting. You can buy this product at most hardware stores or online.
  • A flathead screwdriver
  • Some grit

Step 1: Switch it Off and Flush

The first step is to use the shut-off valve to cut off the water supply from the toilet. 

You’ll then have to access the toilet tank by removing the lid and flushing the toilet to get the water out of the tank. 

Step 2: Get Working 

You’ll need to lift the short arm up and then turn the cap slightly clockwise. 

Then, you should release the arm and lift the cap off of the valve. 

Now you should be able to get the seal out. However, if you’re having trouble, you can always make use of a flathead screwdriver. It does the trick.

Step 3: Get Rid of the Sediment

Turn the water on until it squirts out of the top of the fill valve.

Step 4: Replacing the Seal 

Start by turning the water off, and then remove the cap. You can now slip on the valve seal. Turn it counterclockwise until it fits into place. 

You can turn the water back on and let it return to its average water level.

Fixing Ballcock Fill Valves

These are called ballcocks because they refer to the floating ball from which the cock (valve seat) operates. 

These mechanisms are much easier to work with. However, they’re very prone to issues. 

A simple fix could be to bend the float arm downward, which will help shut off the water at a lower level. 

This fix may not be the solution, especially if you see that water is still running after the flush.

I recommend that you take out the old part and replace it with one of the modern fill versions. Fluidmaster has quite a range to choose from. 

This brings me to my next solution, which will help in situations such as when your toilet fill valve is leaking from the top. 

Replacing Your Toilet Fill Valve

The toilet valve might be leaking from the bottom, but don’t worry. A total replacement will sort that right out. 

What to get:

  • A new fill valve
  • Pliers
  • A bucket
  • A sponge

Step 1: Turning off the Water Supply

Turn off the handle, and flush the toilet to empty out the tank. 

Step 2: Remove the Valve

Using the pliers, disconnect the water supply tube that is attached to the fill valve. Remove the mounting nut as well. 

It should be easy to remove now. 

Step 3: Installing the New Valve 

Put the valve together, if needed. You should also adjust the height, as necessary, for your toilet. 

Despite performing the same function, these can all operate and function a little differently.

new toilet valve example

The instructions for your replacement product are golden here!

Installation is a breeze. Insert the tailpiece into the opening in the tank, tighten the mounting nut, and adjust as needed. 

Put the lid back on, and turn on the water. 

Of course, give your toilet handle a quick push or pull and ensure there’s no leaking or spraying water.

How Do Toilets Work?

Now that you see how to fix your valves, it’s definitely helpful to learn a little bit how toilets work in general to help with any toilet tank issues.

This will help you in this repair (and most of the inevitable repairs to come in the future!).

This video does a good job of explaining it comprehensively:


Why is my new toilet fill valve leaking?

If your brand new toilet seal valve seal is leaking, then it wasn’t installed correctly, or it’s faulty, in which case you should request a refund/swap.

What happens if I don’t fix this type of leak?

Although I always advocate for DIY, if you do struggle and are unable to come up with a solution, you can always contact your local plumber.

Over time, if water is leaking out of the fill valve when you flush each time, this can make a potential mess. 

I once let this issue go, and while the water sprayed up against the tank lid with each flush, eventually the failing part gave way altogether (not to mention, some water escaped and drained down the outside of the tank!).

You’ve Got This. Go Leak Free!

I hope that you now understand how toilets work and are also able to fix your very own. 

A leaking toilet fill valve can be a frustrating thing to deal with. Hopefully, by using my solutions, you’ll be able to come to a resolution.

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