Why Is My Toilet Hissing? | Simple Solutions

Is there a strange snake-like whistling noise coming from your bathroom? Have you got a hissing toilet? What’s going on, is it an emergency, will the bathroom flood!?

Fear not! There’s likely a simple solution!

In this post, I’ll explain why a toilet might be making a hissing sound and how to fix the problem as well as answer some popular questions about the topic.

Let’s dive in!

Why Is My Toilet Hissing?

The most likely cause for a hiss emanating from the tank of your toilet is a leaking inlet fill valve.

If you take the top off the cistern, you will see a tall plastic pipe that is your inlet fill valve assembly. There should not be any water dribbling or spurting out the top of the plastic cover. Water that is properly refilling your tank pours from the side or bottom of the assembly.

The hissing noise happens when water is able to force its way past the valve seal, which results in the hiss. It may stop when the toilet is full again. As time goes by, it will take longer for the hiss to stop until it is constantly leaking.

In order to stop the hiss, you need to repair or replace the inlet fill valve.

Fortunately, cleaning, repairing, or replacing the valve is a reasonably simple DIY fix that you can tackle using your hands and a couple of simple tools.

You can call in a pro. Expect to pay a plumber around £100 to come out plus £50 per hour and the cost of parts.

Hissing toilet - inside toilet tank/cistern looking a inlet fill valve

How to Fix A Hissing Toilet

Step 1: Clean the Inlet Valve and Seal

Sometimes hard water deposits or dirt can get into the inlet fill valve and stop it from fully closing–which leads to that annoying hiss.

  • Turn off the water to the toilet at the shut-off valve/hose.
  • Pop the plastic top off the refill valve pipe.
  • Disconnect the overflow tube running from the valve to the drain pipe.
  • Twist off the top of the valve assembly.
  • Use a soft cloth to wipe away any mould or slime that is present. If you have limescale, use a hard water stain remover. You may need to soak the gasket in the cleaner for an hour to fully eliminate the scale.
  • Reassemble the seal, valve, overflow tube, and cover.
  • Turn on the water and test your repair.
  • If it isn’t hissing, well done! If it is still making that noise, move on to Step 2

Step 2: Replace the Inlet Valve Gasket/Seal

This rubber-type seal can become brittle with age or due to hard water scale.  It may be cracked or torn resulting in that hissing noise. If you cannot completely clean the valve and seal, replacing the part only costs between £2 and £10, depending on the model of your toilet.

After replacing the rubbery part, reassemble your toilet, turn on the water and give it a test.

Is it still hissing and leaking? It’s time to replace the entire valve assembly.

Step 3: Replace the Top Half of the Inlet Valve Assembly

While the cheapest fixes didn’t do the job, replacing your inlet valve will not break the bank, either. Pick up a replacement fill valve for your toilet model online or at the plumbing supply or DIY hardware store. Expect to spend between £15 and £40.

  • Shut off the water
  • Disconnect the overflow tube at the top.
  • Flush the toilet
  • Twist the compression ring at the bottom of the valve assembly and pull the entire section out.
  • You don’t need to replace the tall pipe that remains as it is likely not at fault for your hiss.
  • Pop the new assembly in place and tighten the bottom ring.
  • Reconnect the tube at the top.
  • Turn on the water.

You may need to make a few adjustments to the valve for proper water level refill height for the tank and the bowl. Follow the instructions in the box as each valve type is unique.

Congratulations! Your toilet is no longer hissing!


Should my toilet be hissing?

No, your toilet should not hiss even when refilling the tank. When refilling, you should hear the sound of water running through pipes and maybe a trickling noise in the cistern or bowl.

All sounds should stop as soon as the cistern has reached its fill line. A hissing toilet indicates you have a leaking refill valve.

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Is a hissing toilet wasting water?

A hissing noise in your toilet can indicate you are wasting water. Water is escaping out the top of your refill valve. It may not stop leaking even after your float has reached its shut-off point. That can lead to too much water in the tank which will end up flowing down the overflow pipe, which is wasted water.

If your leak stops about the same time that the refill process does, it is not wasting water now. But these leaks always get worse unless repaired. So, if you don’t fix the hiss, you will waste water.

Is a hissing toilet an emergency?

The snake-like hissing sound emanating from your toilet’s tank is not an emergency. The overflow pipe in the cistern prevents extra water in the tank from flooding your bathroom.

The sound is annoying, and you are wasting water as it will constantly add extra water to the tank. If you are concerned and need to wait to fix the faulty refill valve, you can shut off the supply to the toilet using the valve usually located on the wall behind the toilet.

Just remember to turn it on the next time you visit the loo!

Will A Trickling Toilet Overflow?

No, a toilet that always has a trickle or hiss sound will pour gallons of wasted water down the drain, but it won’t overflow your bathroom. If the leak is in the tank, the extra water runs down the overflow pipe directly to your main waste.

If your bowl always has water leaking into the bowl from the tank, the excess water will push past the trap at the bottom and down the waste. The only ways a toilet will overflow onto the floor is if the toilet bowl is cracked, the floor seal has degraded, or the water supply pipe to the toilet is corroded. Or…if your main waste is blocked, and you try to flush.

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Is A Hissing Toilet Leaking?

Yes, a hissing toilet likely means that the inlet valve is leaking. But don’t worry too much!

It doesn’t mean there’s going to be a flood of water pouring down onto your bathroom floor. The overflow pipe in the toilet tank prevents extra water in the tank from flooding your bathroom.

Final Thoughts…

There you have it! An answer to why your toilet might be hissing and some simple solutions to fix the problem.

While it can be annoying hearing that hissing sound from your toilet, chances are it’s not a major problem or emergency.

Try these easy fixes first before calling the plumber out. You might just save yourself some money and impress your friends with your newly acquired plumbing skills!


Michael R

Michael is a KBB designer from the UK. He's been designing and project managing new Kitchen, Bedroom and Bathroom installations for over eight years now, and before that, he was an electrician and part of a KBB fitting team. He created The Bathroom Blueprint in early 2020.