Toilet Hissing: What it is and How to Fix It

Toilet hissing is a common problem, and when it begins it seems like a small problem that you can just ignore. After all, it is just a small hissing that you can hear when you are in close proximity to the toilet.

Toilet Hissing

However, this problem is not just annoying, it leads to more water usage and high water bills because of constant water drainage. We will take you through all the mechanics to help you better understand the problem and then how to fix it.

Toilet Hissing: What is it?

Toilet Hissing: What is it

In most instances, the toilet hissing noise happens when the toilet is flushed. Excess water or air is moving through the water line into the tank when it should have been cut off. Extra water or air in the line is caused by problems in different toilet components: the fill valve, the float, the flapper, the flapper chain, or the water pressure to the toilet.  

This is a common problem for many older toilets. To put it in simple terms, the hissing noise equals a leaky toilet.  Homeowners can fix the hissing noise with the proper tools, some inexpensive parts, and a bit of time and patience without the need for a plumber.

Understanding How a Toilet Works

Understanding How a Toilet Works

There are two main parts of a toilet: the toilet bowl and the toilet tank and these two components use gravity to help get the job done. The bowl contains the water and connects to the drain. The tank sits behind the bowl and also contains a reserve of water. When someone flushes the toilet, gravity pulls the water down and the tank supplies more water to the bowl.

Flush valve assembly

The flush valve assembly controls the toilet’s flush. The hard plastic or metal assembly is attached to the tank. When the toilet is flushed, the flush valve assembly, also called the ball cock, raises a chain attached to a rubber flapper in order to control the amount of water that goes down into the toilet bowl.

Fill Valve

The fill valve is the mechanism that brings water to fill the toilet tank. As the tank empties, the valve brings more water into the toilet bowl. This valve turns off when the pipes have supplied enough water. If the tank empties for any reason, the fill valve will turn on to maintain an appropriate level of water in the toilet.

A float ball or pressure gauge senses the water supply. Once the float senses there is enough water in the tank, it stops the fill valve. The most common fill valves are the plunger/piston fill valve, the diaphragm fill valve, the float fill valve, and the float-less fill valve.

Rubber Flapper

Rubber Flapper

The flapper, or rubber tank ball, seals the opening that allows water into the bowl from the tank. The rubber flapper breaks the seal between the tank water and the toilet bowl when the toilet is flushed. This brings water into the tank. The flapper stays open until the tank is full and is refilled. The seal shuts once the toilet and tank are full.

Potential Problem Sites in a Hissing Toilet

Potential Problem Sites in a Hissing Toilet

Because the toilet has so many components, there are many potential problems sites that could cause leaks and increase your water bill.

Fill Valve

Over time, sediment and debris can build up on the interior wall of the toilet and deteriorate the fill valve seal causing it to stop working. This allows water to seep through small openings creating a hissing sound. Also, a broken fill valve will cause water to run without stopping in the tank. This causes excess water in the overflow tube or overflow pipe resulting in the hissing noise.


If the float is malfunctioning, it means that it is not turning off the water when the tank has refilled. Therefore, the float will lift the chain on the flapper breaking the seal. When water gets between the flapper and the seal, this leaking water can cause a hissing sound.


A flapper that is in good shape will fit the seal in order to prevent water from seeping through. The flapper is rubber and over time, this can deteriorate or sediment can build up. Either way, the seal is not tight allowing excess water to leak through small openings.

Flapper Chain

The flapper chain attaches the flush valve assembly to the seal. This chain should be the correct size. If the chain is too long, the chain can slip below the seal causing the water seepage. If it is too short, the flapper will not fit against the seal.

Water Supply to the Toilet

Uneven water supply from the water flow lines may also cause a hissing sound as the water tank is refilling.

Diagnosing the Problem

We don’t want you to take your whole toilet apart to find the water leaking culprit. Instead, you can test each component to see which one it is. First, if the problem is the water supply, you will hear the noise when the toilet is flushing. Also, you will see the toilet slow flushing or not flushing all the way. Next, check the fill valve. If this is blocked, the toilet will fill without stopping.

Also, examine the float to see if there are any puncture holes that are causing it to take in water and sink. Further, check the flapper over the seal by closing off the water supply, draining the tank, and unscrewing the flap valve. If it seems dry and brittle or is dirty, this may be the problem. Last, while the tank is dry, check the flapper chain to make sure that it is the proper length.

Fixing the Toilet Hissing Sound

Fixing the Toilet Hissing Sound

In general, this is an easy fix for the amateur plumber. Here are a couple of ways to try to fix the problem.

Fixing a Blocked Fill Valve or Float

Examine the fill valve to determine if this is your problem. First, cut the supply of water to the toilet. Empty the tank by flushing the toilet. Next, remove the valve cap and the valve seal.

Remove any visible debris by rinsing the seal and the valve under running water. If there is still debris on the seal or in the valve, clean it off with more intense cleaning solutions for mineral or calcium deposits. Check the whole mechanism to make sure both are in good shape. If they aren’t, you will need to replace the whole thing. Look to see if the float is damaged. If it is, you should replace it.

Flapper and Chain

Check the flapper and determine if this is the cause of the hissing noise. Next, clean it with water or a mineral cleaning solution. However, replace the flapper if it is warped, misshapen, or not closing well. Also, check the chain to see if it is damaged. If it is, fix or replace it so that it is the correct length.

Related: Why You Should Consider a Bidet Converter Kit

Water Supply  

To fix this problem, you need to locate the water supply valve. Next, adjust the flow until it seems optimal. Test and see if the hissing noise stops and if the toilet flushes better.

Professional Plumbers

If you have tried everything you can and the hissing noise continues, don’t feel embarrassed about calling in a professional to repair the issue. We all know that a bathroom is too important not to work.

Toilet Repair Kits

Toilet Repair Kits

There are other options to repair a hissing toilet. One is a repair kit. These are more expensive, but a good investment. There are different types of repair kits, and they have different parts. The most inclusive is the universal repair kit. Engineers build the universal repair kits together to create a tight seal between the tank and the bowl. This is a good alternative to buying and replacing each component on its own. This kit does away with the float system and replaces it with a large rubber gasket and bolts to create a watertight seal.

There are other kits including fill-valves, fill-valves and flapper combos, silent-fills, and water-saving functionality. Your budget, energy-efficiency goals, and kit flexibility should determine the kit you buy. Also, these kits are easy to install with few tools. Thus, installing them without the help of a plumber is possible.

Keeping Your Toilet Running

Keeping Your Toilet Running

There are a few things that you can do to take the best care of your toilets and prevent future problems from occurring.

  • Clean your toilet on a regular basis.  You will be able to see any problems with your toilet sooner.
  • Fix any problem that you notice as fast as you can. This will save you money on your water bill and preserve the rest of the toilet system.
  • Examine the inner workings of the toilet tank by removing the back lid to see if you notice any problems with the water level, refill valve, the float attached, or the seal.
  • Do not flush anything down the toilet that is not toilet paper and teach any children in the home to do the same. Further, make sure the toilet paper you are using is degradable.
  • If you live in an area with hard water, consider using vinegar from time to time to dissolve the deposits in the water tank that clog up the valves and pipes.

Frequently Asked Questions (FAQ)FAQ

Should my toilet be hissing?

No, if you hear a hissing noise, you need to address the problem as soon as you can.

Is a hissing toilet wasting water?

Yes, a toilet that is hissing has an undiagnosed leak. Leaking toilets can waste several thousands of gallons per month. if your water bill is higher than normal, one of your toilets may be leaking.

Is a hissing toilet an emergency?

A hissing toilet is an indication of a leak but isn’t an emergency.  However, you or a plumber should address this issue as soon as you can get to it.

How much does it cost to get a plumber to fix a hissing toilet?

In general, plumbers charge between $72-$82 dollars per hour not including parts. Because a hissing toilet has different reasons for issues that might be wrong, there is a range of costs for fixing it. On average, it costs between $130-$310 dollars to fix the toilet.

Are some toilets better than others?

Gravity-feed and pressure-assisted are the two most common toilet types in homes. Many plumbers say that gravity-feed toilets with higher tanks are better as the gravity is stronger creating a better flush. The most important thing is to maintain and monitor the toilet you have.

How much does a complete fill valve cost?

Most fill valves cost between $50-$150 dollars.

Why should I just flush toilet paper?

Manufacturers design toilet paper to disintegrate in the water, but other things don’t break down. Items that don’t break down put stress on the toilet as well as the wastewater system.


Toilet hissing can be an annoying and expensive problem that can lead to high water bills. However, it is a problem that is easy to fix by a simple and careful investigation. Once you diagnose the problem, you can fix the problem or call in a professional to do it for you. Either way, you will be more informed about your options and be able to make a well-considered choice.