The Infamous Toilet Hissing Sound, and How to Fix It

Does your toilet make a hissing sound after every flush? Do not worry — there isn’t a scary snake in your commode! Rather, this curious sound is a sign of several potential internal problems with your toilet. While the hiss is likely not a severe problem, without attention, it will not get any better. 

Luckily, these problems are not difficult to fix on your own. 

Toilet smile

The Potential Problem Sites

There are a few intertwined components that can be the cause of the strange hissing noise.

  • Flush Valve
    • Opens the pipe to allow waste and water to leave the bowl.
    • This valve ensures the efficient removal of the water in the bowl when the toilet is flushed.
  • Fill Valve
    • Opens and lets fresh water into the tank. This valve is operated by a float, which follows the water level inside of the tank. 
    • This valve controls the refilling process after the toilet has been flushed.
  • Flapper
    • The flapper is attached to the fill valve. When the flush valve is open, the flapper opens the draining hole and allows water to leave. When the flush valve is closed, the flapper closes the hole and prevents water from draining out.
    • The flapper is a rubber component and, therefore, can be susceptible to wear and tear over time. 

Where Is the Problem?

The problem that causes a hissing noise in your toilet can be due to any one of the flushing mechanisms. Usually, the cause is either the flapper, the flapper chain, or the floater. 

Problems with the Flapper

In order to be effective, the flapper must be the right shape and size. Over time, it is possible that a flapper can lose its shape and no longer create a perfect seal. Normal wear and tear is likely to occur over time. 

First, examine your flapper. If it is dirty or misshapen, you may be able to clean it and adjust it back to order. However, it is possible that you will need to purchase a new flapper. If the flapper is damaged, misshapen, or warped in any unfixable way, you must get a new one. 

When purchasing a new flapper, make sure you know the model of your toilet. You also should know the diameter of the flapper you will need. It must be the right size to seal the drainage hole. Your local hardware store will have a selection of replacement flappers for most varieties of toilets. 

Problems with the Flapper Chain

The flapper chain connects the flush lever and the flapper. It is important that the chain is the correct length. If the chain is too long, it might fall under the flapper and break the seal. If it is too short, the flapper will likely not be able to settle on the drainage hole and create a proper seal. If there is any kind of gap between the flapper and the hole, there will be a hissing sound.

To fix this problem, you can simply unhook the chain and reconnect it to the float at the correct length. You may need to test different lengths and flush the toilet until you find the sweet spot. 

However, if the chain has become old and damaged, you may need a new one. Many chain replacements can be used regardless of your toilet model.

Problems with the Float 

The toilet float controls the flow of water into the toilet tank and stops the flow when the correct level is reached. If the float is not rising to the correct level, it can lift up the flapper above the seal and lead to a hissing noise. 

The float can be damaged by either water leaking into the float or by debris obstructing the path of movement. 

If either of these conditions affects the float, you will need to replace the entire fill valve. Floats are not typically sold on their own. This process can be fairly complicated, so you may want to call a professional plumber. However, it is also possible to buy a replacement fill valve and install it yourself. Doing it yourself will save money. 

Fill valve replacement kits can be found at local hardware stores or online home improvement retailers. It is important to make sure you know what model of toilet you have and check to make sure that the new components will also fit inside of your toilet. Your toilet model number can be found inside the toilet tank. 

Problems with the Fill Valve

It is possible for sediments and debris to build up in the fill valve. Water will be forced through the smaller opening and create a hissing sound. This will also create issues with the speed of flushes and refills in the toilet bowl.

If you notice problems with water flow coinciding with the hissing sound, a buildup of sediment and minerals is likely the cause of your problem.

You can fix this problem by removing the fill valve cap and cleaning out any visible debris. 

How to Clean the Valve

  • Cut off the water supply by turning the water valve off. The water valve can be found at the end of the tube that connects your toilet tank to the wall pipe.
  • Drain the tank by flushing the toilet.
  • Remove the cap from the inlet valve. The inlet valve is inside the tank directly above where the tube connects to the bottom of the tank. The cap may be similar to a medicine bottle cap, and it might require a screwdriver.
  • On the underside of the cap, there will be a seal. Remove the seal and rinse it under water to clean off any debris.
  • Cover up the inlet valve and turn on the water (using the water valve) for a few seconds. Water will flush through the valve and wash out any debris. 
  • Check the seal for holes, tears, or warps. If it is in good condition, put it back in the cap and attach it to the inlet cap once again. 

How to Replace a Seal

You will need to replace the seal if it is damaged. You can either go to the manufacturer’s website and order one or take the seal to your local hardware store. If you bring the seal with you, staff at the hardware store will easily be able to find a match for you. 

With the new seal in hand, you can simply swap it out with the old one. 

If the sediment seems to be too dense and stuck to clean, then you probably have a calcium deposit. Over the years, mineral deposits can grow due to the calcium content in the water. These hardened calcium deposits can be very difficult to clean, and you may want to call a professional. 

Methods to clean a calcium deposit include:

  • Steamer
    • High-power steam can loosen the grip of the deposit and help break it up.
  • High Power Water Spray
    • Spraying water can break apart calcium deposits. Be careful with this method because pressurized water sprays can lead to accidental cracks in the actual pipe. 
  • Cleaners
    • Certain cleaners can be put through the pipes to break down the calcium, such as phosphoric acid, barium nitrate, or white vinegar. These are slow processes, especially the white vinegar. 
    • Be careful using strong cleaners such as bleach. While short term contact with strong chemicals is not damaging to your toilet, extended use of harsh chemicals could lead to problems with the toilet’s internal components. Specifically, rubber parts, such as the flapper, are susceptible to these cleaning products. 

How to Clean Mineral Deposits

Mineral deposits are usually not isolated. If you want to clean a calcium deposit out of your fill valve, it is recommended to clean all other calcium deposits as well. 

  1. Drain your toilet.
    1. Turn off the water supply to your toilet by twisting the water valve counterclockwise. 
    2. Flush the toilet to remove water. You can also use a sponge or towel to dry up the leftover puddles of water in the bottom of the tank. 
    3. You should also use the sponge to dry up any leftover water in the bowl. This water is dirty, so you should use gloves.
  2. Cover the rim jets.
    1. Cover the rim jets with duct tape so that the vinegar will be forced to sit inside the holes and eat away at the mineral deposits.  
  3. Pour the vinegar into the fill valve. 
    1. Pour vinegar into the fill valve so that it can cycle through your toilet. Vinegar will slowly work away at the mineral deposits around your toilet.
    2. Let the vinegar sit for about an hour. If you have a particularly bad buildup of minerals, you can let the vinegar sit overnight. 
    3. Be careful with other cleaning chemicals. You might find recommendations to use harsh cleaners, including bleach. While effective, these cleaners run the risk of damaging the more sensitive parts of your toilet. Harsh cleaners may erode the rubber flapper, which is an integral part of the flushing mechanism. 
  4. Clean the rim jets.
    1. Peel off the duct tape from the holes, and let the vinegar escape.
    2. Use a wire or other small tool to clean around the inside of each rim jet.
    3. Scrape around the inside of the jet hole to clean out mineral buildup
  5. Flush the toilet.
    1. Flushing the toilet will send the used vinegar down the drain and refill the bowl with new vinegar from the tank.
    2. At this time, you may want to use disinfectant to clean the toilet tank.
  6. Add baking soda to the toilet bowl. 
    1. Adding a little at a time, pour one cup of baking soda into the toilet bowl. Because of its chemical properties, there will be a reaction that causes bubbling and fizzling. If you add all of the baking soda at once, it could bubble out of control. For this reason, only add little bits at a time.
    2. You can use this cleaning mixture as a scrub. Clean out any stains or scales of minerals.
  7. Clean the tank.
    1. You can now use a sponge or cleaning brush to scrub any leftover gunk. If you have deposits in your tank or fill valve, you also likely have deposits in other parts of your toilet. Be sure to clean around the bowl and siphon jet. 
  8. Scrub the toilet bowl and jets.
    1. Scrub around the siphon jet at the bottom of your toilet and around the rim jets. Make sure you eliminate stains and bacterial colonies.
  9. Test the toilet.
    1. First, reconnect the water supply by twisting the water valve clockwise into its original position.
    2. Let the tank fill with water.
    3. Give your toilet a flush and see if the water flow and sound has improved.

Still Having Trouble with Hissing Sounds?

If the above methods do not work in your situation, then you will need to replace the entire inlet valve assembly. This process is the most complicated one so far, so there is no shame in calling a plumber. 

You can also choose to do the replacement yourself. This fix does not run the risk of damaging your toilet, but a mistake might break the new valve piece. Inlet valves usually run less than $40, so it is much cheaper than a plumber.

Different inlet valves have different assembly methods, so you should follow the instructions on your particular model. If you do not have the instructions, they can be found on the manufacturer’s website. 

Replacing the valve assembly yourself will take about three hours. It is important to be careful so that you do not accidentally break the new valve. With improper installations, the costs could quickly add up. 

Even Without Hissing, You Could Have Clogs

Hissing is a sign of a calcium deposit creating clogs. However, if your toilet is prone to mineral problems, they are likely to manifest themselves well before the sound occurs. Before you hear the problem, you may notice:

  • Slow refilling of toilet bowl 
  • Weak flushing strength
  • Unusually low water levels in toilet bowl


The sound of a hissing toilet is annoying to everyone, and the cause of the problem is often quite elusive. The source of the issue usually boils down to one of the following situations:

  • Flapper
    • The flapper may be damaged or worn and in need of replacement.
  • Flapper chain
    • The chain may be situated at a length that is either too long or too short.
  • Float
    • The float could be damaged, or its path may be obstructed by debris or other components.
  • Fill valve or related clog
    • Calcium deposits and other debris could limit water supply in the fill valve or other parts of the toilet, creating a hissing sound. 

All of these problems can be fixed on your own at home as outlined in the steps above. However, some problems are difficult for someone without plumbing experience. As such, it is totally reasonable to call a professional plumber and have them find the problem and solve it.

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