Our toilets make an array of sounds during normal operation, from the familiar whoosh of a flush to the gentle gurgle as the tank refills. You’ve likely also noticed that they make an array of unusual noises when something isn’t quite right with the plumbing. For this reason, it’s helpful to pay attention to exactly what your toilet sounds like. One noise you should pay particular attention to is a hissing sound. This persistent hissing can be heard at various times — after flushing, at random intervals, or constantly. No matter when you hear it, a hissing toilet is not something to ignore.
The hissing typically indicates that water is continuously running somewhere it shouldn’t be, which can lead to a host of problems, including shockingly high water bills and potential water damage. For this reason, pinpointing the cause is key to preventing further damage and restoring peace to your home.
The Most Common Reasons Your Toilet Is Hissing
The hissing sound from a toilet is often created by water being forced through a small opening, much like air escaping from a punctured tire. So, in order to stop the noise, you must identify which part of your toilet has failed.
Below, we’ve covered the most common reasons your toilet is hissing and what you can do to fix the problem:
A Faulty Fill Valve
The most frequent culprit behind a hissing toilet tank is a malfunctioning fill valve. The fill valve’s job is to refill the toilet tank with water after each flush and then shut off completely once the water reaches a specific level. When it works correctly, the process is relatively quiet. However, when the fill valve begins to wear out or becomes clogged with mineral deposits or debris, it may fail to close properly.
When the fill valve can’t create a tight seal, water continues to seep into the tank. This continuous flow is forced through the small valve opening, creating the distinct hissing noise you hear. The water level in the tank will rise until it reaches the top of the overflow tube, at which point the excess water will drain down the tube and into the toilet bowl. This cycle of constant refilling and draining is a major source of wasted water, so in addition to hearing constant hissing sounds from your toilet, you may see a large spike in your utility bills.
How to Fix a Faulty Fill Valve:
- Inspect the Fill Valve: Start by removing the toilet tank lid and observing the fill valve (it’s the tall column, usually on the left side of the tank). Look for visible signs of wear, mineral buildup, or damage.
- Adjust the Float: Sometimes, the float arm or float cup connected to the fill valve is set too high, preventing the valve from shutting off. Try gently bending the float arm down (for older ball-style floats) or adjusting the clip on the float cup so that the water level stops about one inch below the top of the overflow tube. Flush the toilet to see if this adjustment solves the hissing.
- Clean the Valve: Mineral deposits can clog the valve. To clean it, turn off the water supply to the toilet using the shut-off valve on the wall behind it. Flush the toilet to empty the tank. Now, you can often remove the cap of the fill valve (check your manufacturer’s instructions) to access the internal diaphragm seal. Rinse the seal under running water to remove any grit or sediment.
- Replace the Fill Valve: If adjusting and cleaning don’t work, the fill valve itself is likely worn out and needs to be replaced. You can do this yourself, or you can hire a plumber to replace the part if that makes you feel more comfortable.
A Worn-Out or Misaligned Flapper
The flapper is the rubber or plastic seal at the bottom of the tank that lifts to allow water to rush into the bowl during a flush and then drops back down to seal the opening, allowing the tank to refill.
Over time, rubber flappers can degrade, warp, or become brittle due to exposure to water and cleaning chemicals. When the flapper doesn’t create a perfect seal against the flush valve seat, water will slowly leak from the tank into the bowl. As the water level in the tank drops, the fill valve will kick on to replace the lost water. This intermittent or constant activation of the fill valve is what causes the hissing sound. You may even hear the toilet hiss for a few seconds every few minutes — this is often called a “phantom flush” and is a classic sign of a bad flapper. By fixing the flapper, you not only stop the annoying hissing but also stop your running toilet and save money on monthly water bills.
How to Fix a Faulty Flapper:
- Perform the Dye Test: To confirm a flapper leak, place a few drops of food coloring or a dye tablet into the toilet tank. Wait for 15-20 minutes without flushing. If you see colored water appearing in the toilet bowl, you have a flapper leak.
- Check the Flapper Chain: Remove the tank lid and inspect the chain connecting the flush lever to the flapper. If the chain is too short, it might be holding the flapper slightly open. If it’s too long, it can get tangled or caught underneath the flapper, preventing a proper seal. Adjust the chain so there is only a slight bit of slack when the flapper is closed.
- Clean the Flapper and Flush Valve Seat: Turn off the water supply and flush the toilet. Reach into the tank and feel the underside of the flapper and the rim of the flush valve seat it rests on. Sometimes, mineral deposits or debris can build up here, preventing a good seal. Use a non-abrasive scrub pad to gently clean both surfaces.
- Replace the Flapper: If the flapper is visibly warped, blistered, or feels stiff, it’s time for a replacement. Installing a new flapper should stop the toilet from making a hissing sound.
High Water Pressure
While internal components are often to blame for a hissing toilet, sometimes the issue comes from other plumbing components. For example, the water supply line that connects to your toilet may be delivering water at a pressure that is too high. Most residential plumbing fixtures, including toilets, are designed to operate within a pressure range of 40-60 PSI (pounds per square inch). If the pressure significantly exceeds this, it can put a strain on the fill valve, and a small amount of water may be forced past the seal, resulting in a constant hissing noise.
How to Address High Water Pressure:
- Test Your Home’s Water Pressure: You can purchase a simple water pressure gauge from a hardware store. Screw it onto an outdoor spigot and turn on the water to get a reading. If the pressure is consistently above 80 PSI, it’s too high for your plumbing system.
- Install or Adjust a Pressure Reducing Valve (PRV): Many homes have a PRV installed where the main water line enters the house. If you have one, it may be set too high or may have failed. You can often adjust it with a wrench. If you don’t have a PRV and your pressure is high, get one installed by a professional plumber. This will not only fix your hissing toilet but also protect all of your pipes and appliances from damage.
Toilet Still Making a Hissing Sound? We Can Help!
If you’ve checked the fill valve, replaced the flapper, and confirmed your water pressure is normal, but your toilet is hissing still, it might be time to call in the professionals. The problem could be a more complex issue, such as a hairline crack in the tank or a damaged overflow tube, which are more difficult to spot and repair.
Fortunately, the expert technicians at Saffer Plumbing have the tools and experience to quickly and accurately diagnose the reason your toilet is hissing. We can then provide a lasting solution, whether it’s a simple part replacement, a more involved plumbing repair, or a full toilet replacement.
For fast, reliable, and professional plumbing services in Baltimore, MD, contact Saffer Plumbing today. We’re here to restore your home’s peace and ensure your bathroom plumbing is working efficiently.