how to fix a hissing toilet
How to fix the common “toilet hissing problem. Source: HGTV

Picture this: you’re going about your day like you always do and everything is well. You wake up, make some coffee, have breakfast, and look through the window to find a beautiful sunny day.

But then you go to the bathroom, flush the toilet and – much to your disbelief – it hisses at you!

Understandably, your first reaction is to be a little mad. I mean, it’s not often you’re having such a nice day and someone is so not having it they actually hiss at you. A snake you could understand because it’s what they do, but even a cat has to be pushed over the edge to hiss!

But, because you're a lady (or gentleman), you do the grown up thing. You take a deep breath and think to yourself:

“Well, if it was upset enough to hiss at me, that means something must be very wrong!

And right you are.

But you have nothing to worry about. This is a common toilet issue and it’s nothing serious – in fact, with a bit of DIY you can fix it in just a few minutes!

So why is my toilet hissing?

The hissing happens because the toilet’s inlet water valve (or a “fill valve) can be partially blocked by bits of sediment settling on the bottom, which compromises the water flow. This forces the water into a narrow stream with added pressure, making it vibrate and sound like a rude “hissing noise.

The “hiss won’t break your toilet and force you to replace it, but if not dealt with, it will continue to get louder as time goes on and the tank will take longer to fill.

How to fix a hissing toilet?

where to locate the inlet valve
The inlet valve on the left and the cap in blue. Source: NOPEC

In practice, all you have to do is flush out whatever small debris are clogging the tank and it will work beautifully (and quietly) again. All you need is a screwdriver and a plastic drinking cup.

  1. First, turn off the water supply to the toilet so we don’t make a mess. Usually it’s located on the hose that connects to the bottom of the tank – simply turn the valve to “off.

  2. Flush the toilet to drain the tank entirely.

  3. Once that’s done, locate the inlet valve and remove the cap from the top. The inlet valve is the vertical device connected to the water supply hose you’ve just turned off. Some might look a bit different, but the cap is usually colored and can be removed by either pressing down and turning or by removing a couple of screws with a screwdriver.

  4. Remove the seal from the underside of the cap – the seal is a rubber or plastic disk.You can easily pry it out with a fingernail or a screwdriver.

  5. Take the seal to a faucet and clean it under flowing water to remove any debris that might have accumulated.

  6. Now take the plastic cup, invert it, and hold it on top of the inlet valve – from where you’ve just removed the cap. We will briefly turn the water supply back on and we’re holding the cup there to prevent water from spraying everywhere.

  7. Turn the water supply on while holding the cup over the inlet valve. Keep it on for 5 to 10 seconds. The purpose of doing this is to let the water flush out any debris from inside the valve. After 10 seconds at the most, turn the water supply off again.

  8. Before moving forwarding, inspect the seal for any rip and tear. If it looks good, you can simply put it back in the cap, and then reattach the cap from where you took it off earlier – basically just put it all back.

  9. Once you’ve assembled everything back, turn on the water supply. Wait for the tank to fill and flush to check if the hissing is gone.

If on Step 8 you noticed the seal was damaged in some way, you will need to replace it. Luckily, you already know how to assemble everything now, so take the seal to your local home improvement center and ask for one that matches.

When you get back home, place it on the cap, place the cap back on the inlet valve, try Step 9 – and that should be the end of it!

However, if after all this your toilet is still hissing, there might be a problem with your inlet valve. In that case, you should call a professional plumber to check it out, because you would need to disassemble even further.


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