How to Fix a Toilet Making a Hissing Sound

A hissing sound coming from your toilet can be annoying and concerning. It usually indicates some type of issue that needs to be addressed. The good news is that most of the potential causes of a hissing toilet are relatively easy fixes. With some basic troubleshooting and toilet parts repair, you can often resolve the problem yourself without having to call a plumber.

What Causes a Toilet to Make a Hissing Sound?

There are a few common culprits behind a hissing toilet:

Sediment Buildup

Over time, hard water deposits, sediment, and mineral deposits can accumulate in the toilet valves and pipes. This buildup causes obstructions and restrictions in the toilet’s water flow. As water tries to work its way through the narrowed passages, it creates turbulence and a hissing noise.

Flapper Valve Issues

Problems with the flapper valve can also result in a hissing toilet. The flapper is the rubber seal at the bottom of the tank that lifts up when you flush, allowing water to empty from the tank into the bowl. If it becomes warped, cracked, or fails to create a tight seal, water will continuously trickle from the tank into the bowl, producing a hissing sound.

Fill Valve Problems

The fill valve is the apparatus in the tank that refills the tank with water after a flush. If the fill valve is not functioning optimally, it may add water too quickly or slowly. This improper fill rate can create turbulence in the tank, leading to a hissing noise.

Loose Connections

The water supply line that runs from the wall to the toilet tank can become loose. This enables water to escape where the connection is loosened, resulting in a hissing leak noise.

Tank Water Level Issues

If the water level in the tank is too high or too low, the changes in tank pressure and water flow can result in audible hissing.

How to Determine the Cause of the Hissing

Start your diagnosis by doing the following:

Listen Closely

See if you can pinpoint the location of the hissing noise. This may help you zero in on the part that is malfunctioning. Hissing coming from the tank likely indicates a problem with the tank valves. Hissing near the base of the toilet may signify an issue with the toilet seal or water supply line.

Check for Visual Signs

Do a visual inspection of the exterior of the toilet to check for water damage or leaks that could be obvious sources of the noise. Also look inside the tank. See if sediment buildup is visible or the flapper looks warped or damaged.

Consider Recent Work

Have you recently jiggled the water supply line when moving the toilet or made other adjustments inside the tank? If so, a loose connection could be allowing water to escape.

Flush the Toilet

Flush the toilet a few times and listen closely to the hissing each time. Pay attention to whether the hissing starts immediately after flushing or if it starts as the tank refills. This may provide clues as to whether the fill valve or flapper valve is the source.

Turn Off Water Supply

Turn off the shut-off valve located under the toilet tank. Wait 30 minutes. Turn the water supply back on and listen. If the hissing returns once you turn the water back on, it likely points to an issue with the fill valve. If it doesn’t return, the culprit may be the flapper valve.

By systematically working through these steps, you should be able to determine why your toilet is hissing. Once you identify the problematic part, you can move on to the repair.

Fixing a Hiss from Sediment Buildup

If sediment deposits appear to be the cause of the hissing noise, here is how to fix it:

Flush the Toilet

Give the toilet a thorough flushing. This may help dislodge some of the loose sediment that has built up.

Use a Tank Cleaning Tablet

Add a tank cleaning tablet to the toilet tank. These tablets contain dissolvable bleach or other cleaning agents that help dissolve mineral deposits and sediment. Allow the tablet to fully dissolve as directed on the packaging. Doing this periodically can help prevent excessive sediment buildup.

Drain the Toilet Tank

If flushing and a cleaning tablet don’t solve the issue, the tank will need to be drained completely so you can manually remove the sediment. Turn off the water supply to the toilet to get started. Flush the toilet to empty the tank. Use a small plastic cup to scoop out any remaining water.

Remove Tank Components

Once the tank is empty, remove all the interior tank parts including the flapper, fill valve, float, and water supply tube. Inspect each part and scrub away any sediment or buildup.

Scrub the Tank

Use a scrub brush or pumice stone to scrub the inside walls of the tank to remove all sediment and buildup. Make sure to scrub thoroughly around the opening at the bottom of the tank where the flapper valve seals.

Rinse the Tank

Once scrubbed, rinse the tank thoroughly with water to wash away all the sediment.


Reinstall all the tank components. Make sure the flapper creates a tight seal and chain length is adjusted properly. Turn water supply back on and allow tank to fill. Flush the toilet again. This should clear out any residual sediment and stop the hissing noise.

Use a Water Softener

To prevent excessive sediment buildup in the future, consider investing in a water softener system if you have hard water. Softening the water makes sediment less likely to adhere to the inner toilet components.

Fixing a Hissing Flapper

If the flapper valve appears faulty, follow these steps:

Inspect the Flapper

Take a close look at the flapper. Check if it is misshapen, cracked, or warped. Also ensure the small overflow tubes are clear of obstructions. If damage is visible, replacement is needed.

Listen for Whistling

If you don’t see obvious damage, listen closely as the tank refills after flushing. If you hear whistling or hissing coming directly from the flapper area, this confirms it needs replacement.

Check the Seal

Remove the flapper and check the sealing surface. Make sure no mineral deposits or grit are interfering with a tight seal. Use a mild abrasive pad to gently polish away any buildup.

Replace the Flapper

Install a new flapper that matches the shape and size of your existing one. Make sure it fully covers the flush valve opening. Readjust the flapper chain length if needed so the flapper can close fully.

Upgrade the Flapper

For a longer-lasting fix, invest in an improved flapper model made of chlorinated rubber instead of traditional rubber. The firmer, more durable material resists warping and deformation.

Use Flapper Lubricant

To extend the lifespan of the flapper, apply a coating of flapper lubricant to the seal surface each time you replace the flapper. This prevents adherence of mineral deposits.

With these steps, a faulty flapper valve that is the source of a toilet hiss should be repaired.

Fixing Fill Valve Issues

If adjustments to the fill valve are needed to stop the hissing noise, here is what to do:

Check the Settings

The most common issue with a fill valve is that it is out of adjustment. First, make sure the float is set to the proper water level in the tank. The correct water level is typically around 1 inch below the overflow tube.

Adjust the Fill Rate

Next, adjust the water flow rate if needed. The fill valve has an adjustment screw to increase or decrease flow. Turn it counterclockwise to reduce water flow or clockwise to increase it. This regulates the speed of tank refilling. Proper adjustment should prevent turbulence and hissing.

Check Refill Tube

Make sure the refill tube that runs from the fill valve into the overflow tube is inserted properly and in good condition. Correct placement muffles the sound of incoming water.

Clean Valve Inlet

Use a stiff brush or wire to gently clean the inlet screen on the fill valve. Make sure no debris is obstructing water flow through the valve. Proper water flow helps minimize noise.

Replace Fill Valve

If adjusting the existing fill valve does not resolve the issue, a replacement fill valve will be required. Match the fill valve style and height of your existing one when choosing a replacement. Install it according to manufacturer instructions.

Use Fill Valve Filter

For recurrent issues, attach a fill valve filter to the water supply line. This filters out grit and particles that could impede smooth operation of the fill valve and cause noise over time.

With these fill valve remedies, any hissing during tank refilling should be eliminated.

Fixing Loose Water Supply Line Connections

If the hissing is coming from the water supply line, try these steps:

Hand Tighten

The water supply line attaches from the shut-off valve to the toilet tank. Tighten this connection by hand using pliers or a wrench to eliminate leakage and hissing. Don’t over tighten.

Tighten Shut-off Valve

Use a wrench to tighten the connection where the supply line hooks into the shut-off valve below the tank. This is another potential source of leaking if loose.

Check Washers

Examine any washers or gaskets along the water supply connections. Replace any that appear cracked, warped, or deteriorated. Proper washers prevent leaks.

Replace Supply Line

If the water supply tube is old or crimped, go ahead and replace it. This will provide optimal water flow and leak prevention. Make sure the new supply line is long enough to reach properly.

Use Thread Tape

When installing supply line connections, wrap plumber’s thread tape 2 to 3 times around threaded ends. This fills in gaps in the threads and prevents leakage points.

With tight and leak-free connections, any hissing sounds originating from this area will cease.

Fixing Problems from Incorrect Water Levels

If the tank water level needs adjustment, take these steps:

Verify Correct Water Level

Make sure the tank water level is right around 1 inch below the overflow tube opening. The float should be adjusted accordingly. Water at the proper level is less likely to make noise.

Adjust Float

If necessary, set the float at the correct level by bending the float rod down or up accordingly. Clamp it in place with pliers once set to proper level to keep it from shifting.

Check Float Operation

Make sure the float can move up and down freely without obstruction. Mineral deposits can sometimes interfere with smooth float operation, leading to intermittent hissing.

Clean Tank

Use a tank cleaning tablet to dissolve any mineral deposits or sediment inside the tank. Proper tank cleaning allows the float to work properly.

Replace Float

If adjusting the existing float does not resolve improper water levels that cause hissing, install a replacement float. Make sure it is sized and shaped appropriately for your toilet tank.

Install Water Level Gauge

For precise water level control, install an adjustable water level gauge. This device allows you to dial in the exact tank level needed to prevent noise.

Careful attention to proper tank water levels should resolve any hissing caused by this issue.

When to Call a Professional Plumber

While most causes of a hissing toilet can be addressed DIY, there are times it makes sense to call in a professional:

  • If you have a very old or unique toilet that requires specialized parts
  • If the toilet tank has atypical components you are unfamiliar with
  • If repeated attempts to fix the issue have failed
  • If you have no time for a DIY repair and need a quick fix
  • If you are not comfortable working with shut-off valves and water supply lines
  • If you determine the source of the noise is due to a problem in the wall or floor

A licensed, experienced plumber will be able to accurately diagnose the hissing, access specialty replacement parts if required, and resolve challenging repair issues beyond the skills of the average homeowner.

While a persistently hissing toilet can be a nuisance, a bit of methodical troubleshooting should help identify solutions. With the steps above, you can resolve many common causes of a hissing toilet quick and easily without paying for a plumber.

FAQs About Fixing a Hissing Toilet

What is the most likely cause of a hissing toilet?

The most common causes of a hissing toilet are problems with the flapper valve, fill valve, or sediment buildup in the tank or pipes.

Why does my toilet hiss when refilling?

If a hissing sound occurs as the toilet tank refills after flushing, it typically points to an issue with the fill valve being out of adjustment or sediment obstructing proper water flow.

Why does my toilet hiss when not in use?

A hissing toilet when not actively being used usually indicates a leak of some type, often due to a faulty flapper valve or loosely connected water supply line. This allows water to continuously escape into the bowl.

How do I know if the flapper is the problem?

You can confirm a faulty flapper valve by listening as the tank refills. If you hear whistling or hissing specifically coming from the flapper area at the bottom of the tank, the flapper needs replacement.

How can I stop my toilet from hissing when refilling?

To stop hissing during refilling, you typically need to clean or adjust the fill valve, replace the flapper seal, and/or clean sediment from the tank and valve components that obstruct smooth water flow.

Why would a water supply line cause hissing?

If the connection where the supply line meets the toilet tank or shut-off valve is loose, it can create turbulence and water escaping as it fills the tank, resulting in audible hissing.

How do I adjust the water level to stop hissing?

Make sure the tank water level is around 1 inch below the overflow tube opening. Adjust the float accordingly and ensure it moves freely without obstruction. A water level gauge can also precisely set the level.

At what point should a professional be called for a hissing toilet?

If DIY troubleshooting does not reveal the cause or repairs do not resolve the issue, the help of a professional plumber may be needed, especially for older or uniquely configured toilets.

Can a water softener help prevent a hissing toilet?

Yes, installing a water softener can minimize sediment buildup inside the tank and on valve components, removing one potential cause of turbulent water flow and hissing.


Annoying hissing from your toilet can disrupt your household’s peace and quiet. While the noise may seem mystifying at first, methodically troubleshooting the potential root causes can reveal issues that often have straightforward DIY solutions. With maintenance like flapper and fill valve replacement, water line tightening, tank cleaning, and float adjustment, you can typically stop the unpleasant hissing and get your toilet functioning normally once again. Paying attention to proper installation and periodic upkeep can help prevent many common causes of a hissing commode.