Toilet Hissing: Understand What It Is and How to Fix It

Recently I had a hissing sound coming from my toilet. This constantly happened for days. I decided to investigate and discovered the problem was inside the toilet tank. Water was squirting from the fill valve. Over time the toilet hissing became worse.

This left me wondering what it is and how to fix it. The hissing is caused by clogging around the fill valve due to debris or other sediments. This increases the water pressure in the valve leading to the hissing sound. You’ll need to clean or replace the valve.

Fixing this problem requires some bit of DIY. Let’s check out what to do if you encounter the hissing sound and what steps to take.

What It Is and How to Fix It?

You might choose to ignore the hissing sound, but it will just get worse. However, below are a few solutions you can manage to do independently.

The fill valve controls the amount of water getting not the tank and limits overflows. The hissing is a result of a faulty valve. 

Clearing the Clog

Toilets have varied designs, which is what you need to understand before embarking on unscrewing your valve.

dismantling fill valve
Image from Duffey Services


  • Switch off the toilet’s water source.
  • Flush the toilet to drain the tanks,
  • Locate the valve and gently unscrew the top of the valve. Some of which don’t require a screwdriver.
  • Identify the cap often rubber and clean it up. 
  • Use a pointed object or water, and clean anything lying underneath.
  • Rinse using clean water to clear any remnants.
  • Clear the link between the water source and the valve. 
  • Covering the valve section with a cup, run water from the source tap and let it clear any clog.
  • Once satisfied with the cleaning, return the valve into position and flush.

Replace Parts of the Valve

If you notice parts of the valve are faulty, plan to replace them rather than replacing the whole fill valve. 

You might find it challenging to identify the right replacement. You can opt to have a sample of the replacement to show the plumber or contact the manufacturer to help you get it right.

Before removing, ensure you’ve closed that water source.

Replacing the Water Valve

new toilet fill valve
Image from Call Our Handyman

You should consider replacing your fill valve if the two options don’t work.

It may appear not very easy to replace and fix everything. However, with proper guidance from a plumber or manufacturer, this can do an awesome DIY project.

Involving a plumber at his point is highly recommended.

Will Cost You to Ignore the Hissing Sound?

You’ll need to get your toilet fixed whenever you hear the hissing sound. However, this issue isn’t an emergency and shouldn’t cut short your plans.

The major cost might be an increased water bill since the water from the valve often leaks.

The best thing would be to ascertain the extent of the damage to help you make concrete decisions.

How to Deal With Constant Hissing Sound?

If the toilet is consistently hissing, the problem could be caused by the toilet inter water valve. Bits of silt or hard water might accumulate in the valve over time and usage. 

clogged fill valve
Image from Chris Banks

The water flowing into the tank is partially blocked as a consequence.

It causes an increase in water pressure in the valve, which forces the water out in a narrow stream, causing the toilet to hiss.

Does the Hissing Sound Indicate Leakage?

You’ve figured out by now that the fill valve causes the hissing.

Occasionally you’ll also notice that the tank is full and water is leaking into the overflow tube. That’s a leaking tap. 

It could be a faulty fill valve, but it’s more likely a misaligned float. If there isn’t any water spilling into the overflow tube, the hissing could be caused by air pressure.

The toilet isn’t leaking in due to hissing, but something is wrong.

What Are the Other Noises to Look Out For?

When your toilet starts making weird noises, it can be alarming, especially if it’s one you’ve never heard before. 

However, determining when a toilet noise requires contacting a plumber can be tedious and problematic. 

Here are some common toilet noises to help you figure out what’s wrong with your plumbing.

Water hammerWater flow suddenly haltedRegulating the fill valve. Adjusting the shut-off valve.
High pitch whistleFaulty ballock systemAdjusting the existing ballcock valve. Replacing the existing ballcock mechanism.
Ghost flushingDefective FlapperReplacing the toilet flapper
Toilet gurglingBlocked sewer drainCall a professional plumber 
Toilet Makes Loud Noise RandomlyLoose washer in the ballcock systemReplace the fill valve assembly.
Toilet Making Noise When Not In UseWorn out FlapperReplace the flapper.
Toilet Noise After FlushingLeak in the system.Buildup debris in your pipes.Toilet replacement.
Toilet Whistles When FlushedAir or water leak in the fill valve.Replace the fill valve. 
Call a plumber.


A defective fill valve is the most common cause of a modest hissing sound in the toilet tank. 

replacing fill valve
Image from To lists Handyman Services

If left unchecked, the volume of running water might quickly accumulate. 

As a result, it’s critical to solve your hissing noise. 

Turn off the toilet’s water supply valve if you hear a noise. This will keep any extra water out of the toilet and allow you to schedule a time to fix the problem. 

If this is your only toilet and it still has to be used, you can turn the valve off and turn it on when flushing the toilet.

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