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Why Is My Water Heater Hissing?

Troubleshooting from George Brazil


If your water heater is making a hissing noise, it could be due to:

  • Condensation hitting hot surfaces during refills
  • Leaks or fractures in the tank
  • The temperature being set too high
  • Sediment buildup

Don’t worry, we’ll take a look at each of the above situations and explain whether it’s normal or whether you have a water heater problem that needs professional repair.

Need water heater help right away? Just contact us. We respond right away for fast plumbing help.

Condensation hitting hot surfaces during refills

If you hear the hissing noises after using large amounts of hot water (like after showering or using the dishwasher), the noise is most likely normal.

Why? Well, when a large amount of hot water is used, cold water enters the tank to fill it back up. And when cold water enters the hot tank it can produce condensation on the outer surface of the tank. (Think of how a cold glass of water beads up on a hot summer day.)

When that condensation rolls down the side of the water heater and hits hot surfaces (such as parts in or near the burner), it will sizzle, producing a hissing sound.

The amount of condensation rolling down the side of the heater determines how loud the hissing sound will be. And how long it takes your tank to heat up the water determines how long you’ll hear the hissing sounds.

You can expect higher amounts of condensation when:

  • The water heater is undersized for your household’s hot water needs
  • The incoming water is at its coldest temperatures (winter and early spring months)

Fracture or small leak in the tank

Just like condensation, if you have a fracture or leak in your tank, water will escape and hit hot surfaces, producing a hissing/sizzling sound.

So how do you know when you have a fracture/leak in your tank or when it’s just condensation? Well, if you hear the sizzling sounds constantly (and not just after large hot water draws), you might have a fracture or leak in your tank.

Also, keep an eye out for large puddles of water collecting underneath the tank. If you have a small fracture or leak, it’s only going to get bigger over time and eventually lead to large amounts of water leakage (and eventually bursting).

Temperature set too high

If you find that your water heater’s temperature and pressure (T&P) valve is producing a hissing noise, your water heater output temperature might be set too high.

You see, your T&P valve is a safety valve that opens automatically when pressure inside your water heater reaches a dangerous level. And when the valve releases this pressure, it can sometimes produce a slight hissing noise.

So what does pressure have to do with high temperatures? Well, a lot. You see, the hotter the water in your water heater, the more pressure accumulates inside the tank. So if your water heater temperature is too high (140 degrees or higher) we suggest lowering the temperature to around 120 degrees. Don’t go lower than that or bacteria can start thriving in the water.

Sediment buildup

If you hear a rumbling or popping noise along with the hissing sounds, you most likely have sediment buildup and need to have your water heater flushed.

So, what is sediment buildup and what does it have to do with your hissing water heater? Well, first off, sediment buildup happens when the minerals in the water settle on the bottom of the water heater tank. This is especially a problem in Arizona because our “hard” water has a high number of minerals.

And as this layer of minerals thickens, it traps water bubbles that get superheated and boils to steam at the bottom of the tank (producing a sizzling noise). This can also happen as a result of lime buildup on the heating elements.

Have a professional inspect your tank to determine whether your elements need to be replaced or whether you need a water heater flush.

Need help from an AZ plumber?

If you need a professional to inspect your hissing water heater, just contact us.

We’ll send over a plumber as soon as possible to inspect the system and give you your best options.

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