Why Is My Toilet Making a Hissing Sound?

Fixing Hissing Toilet

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A toilet making a hissing sound is annoying to residents, and it's even a nuisance when the toilet shares walls with neighbors. Depending on which part of the toilet is causing the hissing, the toilet might also be wasting water, too. Learn how a toilet makes hissing sounds, plus the easy, quick, and inexpensive DIY ways to eliminate the hiss.

Toilet Flush Chain Is Sized Incorrectly or Damaged

The flapper at the bottom of the toilet tank needs to be fully shut after every flush to keep the next cycle of water in the tank. A chain is attached to the top of the flapper. The other end of the chain is attached to the extension arm of the toilet handle.

A toilet makes a hissing sound when the chain prevents the flapper from closing or when the chain is so long that excess chain gets caught under the flapper. A chain that is too short will keep the flapper in a slightly raised position, allowing water to pass out of the tank—creating a toilet hissing sound.

How to Fix a Toilet Flush Chain

The toilet flush chain might just be twisted up and shortened or it may have been improperly sized when it was installed. In this case, the chain can be adjusted. If the chain is damaged, it can be replaced. A replacement toilet chain costs $2 to $3.

  1. Remove the toilet tank lid and put it aside.
  2. With a flashlight, observe the chain. The chain should not be twisted or bunched up, nor should it be caught on any other toilet components.
  3. If the chain is twisted, straighten it out it while it's still in place.
  4. If straightening the chain doesn't work, turn off the toilet water supply. Flush the toilet to remove the water from the tank.
  5. Readjust the toilet chain to the correct length: long enough to allow the flapper to close but not so long that it twists up or gets trapped under the flapper.
  6. A chain that is old, rusted, or mangled is more prone to twisting up than a new, smooth chain. If the chain is old or damaged, replace it entirely.

Flap Valve and Seal Are Dirty

The flap valve is a hinged flapper at the bottom of the toilet tank that lifts on command to permit water to flow into the towel bowl. The flap valve is blue, red, gray, or black, and it might be hard plastic or made of soft silicone or rubber.

Over years of being immersed in water, the flap valve and the seal below it can build up slime, sediment, mold, and other debris. If one is dirty, usually both are dirty since they touch each other. This gunk allows traces of water to flow into the toilet bowl, creating toilet hissing sounds.

How to Repair a Dirty Flap Valve and Seal

  1. Turn off the water supply to the tank by turning the shut-off valve near the floor clockwise.
  2. Flush the toilet to drain water from the tank.
  3. Lift the toilet lid off and set it aside.
  4. Carefully dry off the bottom of the tank with a hand towel.
  5. By hand, lift up the hinged flapper at the bottom of the tank. With a flashlight, inspect the bottom of the flapper and the rubber or silicone seal below it. Neither should have grime, sediment, or slime. If they do, they need to be cleaned.
  6. Use a non-abrasive kitchen scrubbing pad to scrub off particles.
  7. Follow by cleaning with a cloth dipped in warm water.
  8. Drop the flapper back in place, turn on the water, and let the tank fill.

Flap Valve and Seal Are Cracked or Deteriorated

The hinged flapper at the bottom of the toilet tank opens to let the water rush into the toilet bowl or closes to let the toilet tank fill up again. Because the flapper and the seal are made of rubber or silicone, these components are prone to cracking or otherwise deteriorating over time.

Toilet hissing sounds are created by water slowly leaking through cracks in the components or between a damaged flapper and seal.

How to Replace a Cracked or Deteriorated Flap Valve

When the toilet flap valve and seal are damaged, they cannot be fixed. Instead, the toilet flapper and seal must be replaced. Use a universal 2-inch toilet flush valve repair kit, an item that costs $10 to $15. The kit usually includes a toilet flapper, seal, sealant, and sometimes a chain.

  1. Turn the toilet shut-off valve clockwise to turn it off.
  2. Flush the toilet.
  3. Remove the toilet tank lid and put it safely aside.
  4. Dry off the bottom of the toilet tank with a towel or hair dryer.
  5. Remove the old toilet flapper. Unclip the chain from the old flapper. Leave the other end of the chain attached to the toilet handle arm. Pegs extend from the sides of the flush valve tube. Remove the flapper ears from those pegs.
  6. Remove the old seal.
  7. Install the new toilet flapper by fitting the ears of the new flapper over the pegs on the flush valve tube.
  8. Attach the chain to the new flapper.
  9. Test-flush the toilet (while still dry) and observe the chain lifting the flapper. The chain should not have so much slack that it gets twisted. Yet if the chain is too tight, it will not allow the flapper to complete the seal. Adjust the chain longer or shorter as needed.
  10. Close the tank lid and turn the water back on.