Toilet Is Making Hissing Sound When Flushing? (Fix It Now!)

Ryan Womeldorf
by Ryan Womeldorf

When it comes to household issues, few are quite as frustrating as dealing with a malfunctioning toilet. There can be a plethora of issues with plumbing throughout the life of a home and dealing with your toilet is probably the last thing you want to address.

Perhaps you have been hearing a hissing sound, something akin to a loud snake, when you flush. What’s the problem there? Well, the most likely culprit is that the fill valve has either become blocked up or broken entirely. In some cases, you can get away with cleaning it. In others, you will need to replace the fill valve entirely.

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Why is the Toilet Hissing?

Hearing a hissing noise emanating from the toilet may not be cause for dire concern but it certainly is not a pleasant noise. It sounds similar to a really big snake being vocal in your bathroom. But why is your toilet doing that in the first place?

Water pressure. The inlet water valve, also known as the fill valve, is typically the cause. Hard water deposits can and will build up over time. They settle into the valve and then block the flow of water going into the tank. That obstruction increases the water pressure within the valve.

That build-up of water pressure forces the water out through a narrower stream, which causes the hissing noise you hear as well as slow flushing. It won’t necessarily do damage to the toilet, but it definitely will not go away on its own.

Clean/Fix the Fill Valve

The good news is that there is a simple DIY fix to get rid of that hissing noise. Even further good news is that you do not have to replace the toilet. More often than not, it is as simple as cleaning and sealing the inlet valve.

How to Clean and Seal the Inlet Valve

When debris and sediment wind up clogging up the valve, then it can be as simple as flushing it out. Thankfully, this process is a quick one; about 15 minutes in total. All you need is a plastic cup and maybe a screwdriver to get the job done.

  • Turn off the water. Cut the water supply to the toilet. There is a hose that runs into the bottom of the toilet’s tank. Find the valve and turn it to the “OFF” position.
  • Flush the toilet and locate the inlet valve. Give the toilet a flush in order to drain the tank. Then, find the inlet valve. It is the vertical assembly right above where the water supply hose runs into the bottom of the toilet tank. Take the cap off the top of the valve. Your design may vary, but the cap can be removed by pushing and twisting or by taking out a screw or two using your screwdriver.
  • Remove the seal. On the underside of the cap is a rubber seal. Pry it out and rinse it off. This should remove any potential debris that can accumulate beneath.
  • The plastic cup. Invert the plastic cup and put it over top of the now capless inlet valve. Hold it there as you turn the water back on to keep the water from spraying out at you.
  • Hold for 5-10 seconds. Holding the cup over the valve, turn the water back on. The water should flush out any debris that can become trapped within the valve. Take a good look at the seal for any tears, rips, or warping. If it is damaged, you will need further repair. If not, reattach it and the cap to the inlet valve.

When the Seal is Damaged

It is important that you inspect the seal inside of the inlet valve cap. Make sure that there is no damage or warping, otherwise it will not seal properly. If you notice damage, that could potentially be the reason for the toilet hissing.

The good news is that replacing it is relatively easy. You can opt to go through the manufacturer for a new one. The easiest solution is to just take the old one to a local hardware store and find a new one that matches. All you have to do is put the new seal in place of the old one and the inlet valve assembly should work fine again.

If the Hissing Persists

So, you’ve tried flushing. You’ve tried replacing the valve seal. Still, the hissing continues. If you have gotten this far, it could be that the valve assembly needs replacing. The most likely reason is that hard water formed down in the lower part of the inlet valve assembly.

When that hard water deposit forms, the only way to resolve the issue is to completely replace the valve assembly. This can be something of a complicated fix. Unless you have experience with more complicated toilet repairs, this one may be best left to the professionals.

Replacing the Inlet Valve Assembly

Should you be insistent on tackling the assembly replacement, there are a few helpful steps to follow. The good news is that you can’t do any damage to the toilet if you botch the fix. The bad news is that breaking a replacement valve assembly means you have to replace it. Keep that in mind.

  • Get the tools. To perform the assembly replacement, you will need an adjustable crescent wrench and a pair of water-pump pliers. For an experienced DIYer, it should take a few hours. If you are less experienced, it is okay to take longer.
  • Remove the old assembly. This can depend on your model, but there are typically a few key points. You will have to remove the vertical valve assembly, disengage it from the toilet’s flushing level, and disengage it from the arm responsible for lifting the rubber stopper that seals water into the tank. If you are uncertain of how to do this, check the manufacturer’s website.
  • Get a new kit. Take the old valve assembly out and take it with you to a plumbing store or home improvement center. Buy the replacement that matches up with the one you have. The kits come with nuts, washers, and even seals needed to perform the new installation.
  • Follow the instructions. The valve assembly kit should also have instructions for installation. It should also tell you how to properly adjust the water height within the tank.

What About Other Noises?

Unfortunately, hissing is not the only problem you may run into. There are a few different sounds to contend with. You may even run into something known as ghost flushing. These are all relatively normal and explainable. Even better, they all have solutions that you can implement to get rid of the issue.

In general, there are a few common causes. The aforementioned fill valve, a leaking toilet valve, or mineral buildup somewhere within the system.

Toilet Whistles or Makes a High-Pitched Squeal

You may notice that when you flush the toilet, it makes a high-pitched squeal when the tank is in the process of refilling. While that kind of noise can certainly be alarming, there is no need to panic. The simplest explanation is that the ballcock valve, which is known as the float valve, is off or damaged.

  • Inspect the valve. In most cases, you can simply adjust the float valve to achieve the desired results. Take a look and make sure that it is in the proper position.
  • Replace if adjusting doesn’t work. The good news is that the float valve is relatively cheap to replace. Don’t bother replacing individual components; replace the entire unit. It is simple enough that most DIYers can do it, though a qualified plumber will typically get the job done sooner.

The good news here is that, like the inlet valve, amateurs can’t do any damage implementing repairs. This can make for a good practice run for amateur DIYers.

Toilet Gurgles When Flushing

This can be a more troublesome issue because it is typically a bit tougher to find the source of the problem. Gurgling can be due to a blockage in the sewer drain, in a vent stack, or even in the actual toilet.

A gurgling noise coming from your toilet should be addressed by a professional plumber. Try to avoid using the toilet until you can bring someone in to take a look. Gurgling can start as a simple annoyance before turning into a major issue in no time.

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Ghost Flushing

This one tends to cause a few jumps. For whatever reason, right in the middle of the night, the ghost can seemingly flush on its own. The good news is that you don’t have a ghost problem and the actual explanation is a simple one.

A bad flapper. The most likely cause is that the water in the tank is slowly seeping out. The most likely source for the breach is an issue with the flapper. When the float gets down below a particular level, the water will switch on. Before you know it, it seems like the toilet is flushing on its own.

Inspecting and fixing. To find out if the flapper is the issue, it is as simple as using food dye. Give it about 30 minutes and look to see if any of that food coloring has made its way into the bowl. If you see color, replace the flapper.

The good news is that flappers are not only inexpensive to purchase, but they can be replaced by even the most novice of DIY types. Turn off the water, disconnect and remove the old flapper, and install the new flapper. It is as simple as that to replace.

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Ryan Womeldorf
Ryan Womeldorf

Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.

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