A hissing toilet is a common phenomenon in most households, especially in older homes that have seen better days. The toilet hissing can be loud and disruptive, like a reptile invasion has taken over your bathroom. A toilet constantly hissing might persist for a long time, annoying you on a regular basis. Plus, the weird noises can sound quite spooky, especially if you are alone in the house.

You will be glad to know that the toilet hissing noise can be fixed easily by a plumber. A toilet making noise isn’t a particularly severe problem, so it can be resolved if you have the right tools and replacement parts. A quick tip before we delve deeper into the hissing toilet situation: the problem is most likely an incorrectly installed flush valve, which could be allowing leaks from the tank into the toilet bowl.

Of course, there might be other causes that lead to the toilet making weird noises. Here are some common explanations for why your toilet occasionally hisses:

1. The toilet is hissing because of an uneven water flow.

Let’s say you have just flushed the toilet, and the water has started flowing into the tank. As the tank is refilling, you hear a loud toilet hissing noise. The culprit is usually uneven water flow from the supply line. Along with the toilet making noise, you may also notice it is slow at flushing or it is not flushing fully.

To fix this problem, reduce the volume of water flowing inside the pipe. Start by checking beside or under the toilet tank to locate the supply valve. Then, adjust it accordingly until you have the optimal water flow.

2. The toilet is hissing because of a blocked fill valve.

A fill valve ensures that water stays at the correct level in your toilet tank. When the fill valve is obstructed or blocked, it runs water into the toilet continuously. A blocked fill valve may be caused by wear and tear, incorrect calibration, or sediment build-up. Any of these reasons could result in an overfilled toilet tank. As the excess water flows into the overflow pipe, it produces a toilet hissing noise.

The good news is that you can fix this problem easily. Just replace or recalibrate the valves and you will be good to go. To adjust the water level and stop the overflow, make sure the float sits under the overflow pipe. Once you fixed the fill valve, the toilet should stop making weird noises.

3. The toilet is hissing because of a flap valve seal covered with sediment.

If your toilet occasionally hisses, check the flap valve. This is the apparatus that allows water into the toilet tank every time you flush. The flap valve has a seal that regulates the water levels when your toilet is not in use. With time, the flap valve seal could become brittle or get covered with sediments. As the valve loses effectiveness, water might leak into the bowl, which produces a toilet hissing noise.

Cleaning the seal and the flap valve may be enough to fix this problem. Just shut off the water supply to the tank and unscrew the flap valve at the bottom of the toilet bowl. Clean the seal using a sponge and a mild detergent. If the seal is cracked or compromised in any way, call a plumber to have this part replaced.

4. The toilet is hissing because of high water pressure.

Let’s go through another scenario, where you have just finished your business on the toilet. You flush the toilet, only to hear a loud banging sound. Often called the “water hammer”, this sound is caused by high water pressure coming from the supply lines. It may also indicate restricted water pressure in your toilet.

High water pressure from the water heater or the pressure tank causes your toilet to release the pent-up pressure, which results in a loud banging noise. You can fix this problem by easing off the water pressure inside the pipes. There is a valve for this near the main supply line. The recommended water pressure is between 30 and 35 psi. To correct this problem, use a screwdriver to reduce the pressure level accordingly.

5. The toilet is hissing because of an incorrectly installed refill tube.

You can find the water refill tube above the overflow pipe. If improperly installed, it may result in what is known as ‘ghost flushing’. The flushing, of course, has nothing to do with ghosts in your toilet. Rather, the toilet flushes as if someone has just used it, but in reality, no one is there. The situation can resemble a spooky horror movie, where the toilet flushes out of nowhere.

To fix the phantom flushing issue, repair the flapper. To do this, reposition the refill tube and adjust the chain, or replace the entire component. If the toilet is still making weird noises, contact your plumber to have it properly fixed.

6. The toilet is hissing because of a damaged float.

That round plastic piece in your toilet filled with air is called a float. You can find this component at the back of your toilet. A float signals the fill valve when to shut off. When the float is compromised, it cannot carry out this critical task. The result is that the fill valve cannot shut off, which might cause a toilet to make constantly hissing noises.

The most likely scenario is that the float has punctured or split apart. When this happens, water ends up leaking into the float and weighs it down. To establish if your float is damaged, pour water into the sump pump basin until it floats. If it stays under, the float is faulty and should be replaced.