Is Your Toilet Making A Hissing Sound | Fix It

When you hear a hissing sound coming from your toilet, it’s not just annoying; it’s a sign that something is wrong. You may not see any leaks, but that doesn’t mean there isn’t water wasting away, running up your utility bills, and damaging your home. 

A hissing toilet can be caused by one or more reasons, such as a damaged flapper, a faulty fill valve, a blocked water supply line, or even a crack in the tank or bowl. In this article, we’ll explore the most common causes of a hissing toilet, explain how to diagnose and fix them, and give you tips to prevent future problems. With our help, you can rest assured that your toilet will flush quietly and efficiently.

What’s Making That Hissing Sound

This hissing noise you hear coming from your toilet is caused by air or water escaping where or when it shouldn’t. The most common cause of this is a faulty fill valve, which is located inside the toilet tank. The fill valve controls how much water enters the tank with each flush. If too much or too little water flows into the tank, the toilet won’t work properly. 

A bad fill valve can sometimes allow more water than it should enter the tank. When this happens, a hissing sound might occur as water continues to flow after the flush is complete. You can diagnose this issue by removing the tank cover and locating the overflow tube. 

If excess water is flowing into it, this is the cause of the hissing noise. In this case, the fill valve is faulty, and you will want to get it fixed as quickly as possible because all that water flowing down the overflow tube is costing you extra money every month. 

On the other hand, if the water level in your toilet tank falls where it should and no water is flowing into the overflow tube, the hissing sound could be caused by an issue with the water supply coming into the tank, air in the plumbing, or a leak somewhere behind a wall. 

A licensed plumber will be able to diagnose the problem and get it fixed for you. Don’t put off scheduling a plumber because if the problem is a leak behind the wall, you could end up with major damage or a more costly repair at a later date. 

Different Types of Toilet Hissing

There are different types of toilet hisses. Identifying the type of hissing sound your toilet is making can help you diagnose the cause, so you can fix it properly. 

Hisses Randomly Every Few Minutes

A toilet that randomly hisses every few minutes is probably an older model with a metal ball cock fill valve. The issue happens when the washer in the ball cock unit gets worn out. You can try tightening the washer, but if that doesn’t work, you will need to replace the entire fill valve assembly. 

Constant Hissing Noise

A constant hissing noise from your toilet might have something to do with the water valve that allows water to flow into the tank. If you have hard water, or your toilet is older, sediment or mineral deposits have likely settled in or on the fill valve, causing a partial blockage. Often, the blockage will cause the water to shoot into the tank rather than to flow, which in turn, causes the hissing sound. 

Toilet Hissing and Not Flushing

A hissing toilet that does not flush is a sign that something is broken or disconnected inside the tank. The likely cause is the flapper chain. The flapper chain is the metal or plastic chain that raises and lowers the rubber flapper at the bottom of the tank each time the toilet is flushed. The chain must be the exact correct length so that the flapper can open, close, and seal properly. 

If the chain is too short, it won’t let the flapper close completely, allowing water to run constantly, and thus, making a hissing noise when the commode should be quiet. Take the cover off the tank, inspect the flapper chain, and adjust it as necessary to allow the flapper to operate correctly. 

Toilet is Hissing and Leaking

Toilets make all kinds of strange noises including gurgling, screaming, sloshing, bubbling, and hissing. These noises are usually caused by the passage of air or water as it escapes the fill valve. If the valve isn’t functioning properly, the toilet may make a hissing sound and leak. In the next section, I’m going to tell you how to stop your toilet from hissing. 

How to Stop Your Toilet from Hissing

Now that you can identify which type of hissing sound your toilet is making, here’s how you can make it stop. 

Cleaning The Refill Valve and Seal

Fixing your hissing toilet is going to require a little bit of elbow grease. If you don’t mind that, get yourself a plastic drinking cup and a screwdriver or two and follow the steps below to fix the issue yourself. 

Step 1: Turn Off The Water Supply

Locate the water supply valve underneath your toilet’s tank. Turn it all the way clockwise to shut the water off. 

Step 2: Flush The Toilet To Drain The Tank

With the water turned off, flush the toilet. This will drain the tank so you can work inside it. 

Step 3: Locate The Inlet Valve

Identify the inlet valve. It is a vertical tube that sits directly above where the water supply hose is attached to the bottom of the tank. The inlet valve will have a cap on it that you can remove by either pressing and twisting (like a child-proof cap) or removing a couple of screws with a screwdriver. 

Step 4: Remove The Seal

Inside the cap is a rubber or plastic seal. Remove it carefully using a flat-head screwdriver or your fingernail. Rinse the seal with water to remove any grime or buildup that may be present. 

Step 5: Invert The Plastic Cup 

Turn the plastic drinking cup upside down and hold it over the fill valve (where you took the cap off). In the next step, you will turn the water back on, and the cup will help keep most of the water from splashing everywhere. 

Step 6: Flush Debris Out Of the Valve

Holding the cup directly and firmly over the fill valve, turn the water supply back on for 5-10 seconds. The stream of water should dislodge and remove any debris that has built up inside the valve. 

Turn the water back off and inspect the washer/seal you rinsed off earlier. Look for signs of wear. If it looks good, replace it in the cap and put the cap back on. If it looks to be cracked, warped, or damaged in any way, head to your local hardware store for a replacement. 

If cleaning the fill valve doesn’t resolve the hissing sound, move on to the next option: replacing the refill valve. 

Replace The Refill Valve

If your toilet is still making a hissing sound after cleaning the refill valve, you will need to replace the valve itself to stop the noise. The mineral buildup has likely damaged the old valve, and the only way to get rid of the noise is to put in a new one. This fix is a little more complicated than cleaning the fill valve, so you may choose to call a plumber to repair it. If, on the other hand, you fancy yourself an avid DIYer, feel free to tackle the fix yourself. 

Every toilet is different, so you should consult the toilet manufacturer’s website for directions on removing an old fill valve and installing a new one. The repair will involve several steps including disconnecting the valve assembly from the flush mechanism as well as the rod that lifts the flapper when you flush. If you take the old valve assembly with you to the hardware store, you should be able to purchase a fill valve kit with instructions that will help you install the part and adjust the water level in the tank. 

FAQs Toilet Making A Hissing Sound

Is a hissing toilet an emergency?

It depends. If the hissing is caused by a faulty fill valve, the worst thing that happens is your toilet uses extra water, which wastes water and increases your water bill. If, on the other hand, the hissing sound is caused by a water leak somewhere in your toilet’s plumbing, it should be addressed ASAP as it could cause expensive damage to your home. 

How much does it cost to fix a hissing toilet?

If you replace the fill valve yourself, you can expect to pay anywhere from $19-$35 for the parts. This fix should take no more than 3 hours to complete. 

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Having renovated two homes and completed countless repairs, it was time to share this experience with the world. From repairing kitchen appliances to remodeling entire homes, my 30 years of experience will hopefully help you on your journey to a beautiful and functional home

Plumber and HVAC Technician | Website | + posts

As a retired Master Plumber Jamie has over 30 years of hands-on experience, making his plumbing knowledge second to none. He has also worked on both residential and commercial HVAC installation and repair projects.