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Why Is My Water Heater Hissing?

Worker Set Up Electric Heating Boiler At Home.

Whether you have a tank or tankless water heater, you need it to sail through the winter season. The water heater helps ensure the shower water is hot when needed.

It keeps the water at a more or less constant elevated temperature. So, it’s understandable if you are considering the water heater is making a hiding noise considering the water in it is scalding. So, why is your water heater hissing?


When your water heater makes a hissing sound, it could indicate a big problem that requires repair or replacement. But sometimes, the hissing noise is normal or only requires a simple fix. Some common reasons for the hissing noise from a water heater include:

  • The water tank is leaking,
  • The temperature is too high,
  • Condensation,
  • Sediment build-up.

Please take caution when inspecting the cause of the hissing noise on a water heater as it contains hot water at high pressure, which can cause serious injury.

This article will cover the main reasons your water heater is making a hissing noise. We will also educate you on what you can do in each case to help solve the problem.

4 Reasons Your Water Heater Is Hissing

If your water heater is hissing, the first thing you want to do is to figure out the cause of the hissing. Based on your findings, you can find the best solution to stop the noise, hopefully forever.

Inspecting a water heater when it is still functional or hot can cause potential safety hazards. Always power off the water heater before working on it. Below are possible causes why a water heater is hissing and how to fix it.

1. Water Tank Is Leaking

Water Underneath A Water Heater Shows The Beginning Of A Leak, Also Shown By The Signs Of Rust Around The Bottom Rim, With Selective Focus On The Water, And Dirty Hoses Blurred In The Foreground

If you notice the water heater is hissing all day, regardless of whether it is in use or empty, it could be that the tank is leaking. In such a case, it’s best to fix the issue as soon as possible.

The leaking water heater tank can spike your water bill if it leaks two gallons an hour, meaning 48 gallons of water is wasted daily.

The longer you wait to address the issue, the wider the leak gets, leading to more wastage of water. When you inspect the take to be sure it is leaking, look for a pool of water.

Or you can check the tank’s body, and if you see steam oozing, the tank is leaking. If you have confirmed the tank is leaking, you should contact a professional to assist with the replacement.

2. Temperature Is Too High

The Temperature Setting On This Water Heater Is Set At 45 Degrees. Translation: Operating. Priority.

Another possible reason your water heater is hissing is that the temperature is too high. When the temperature is set too high, it causes the pressure in the tank increases to a point where the safety valve opens to release the pressure.

Otherwise, the pressure in the tank will build up to an extent the tank will explode.

So, to fix this issue, you should turn down the water heater’s temperature. You should set the water heater to 140 Fahrenheit only when multiple users are using the shower simultaneously.

Otherwise, setting the water heater at 120 Fahrenheit or lower is ideal. But don’t go below that 120 Fahrenheit mark, as anything lower than this will facilitate bacterial growth.

3. Condensation

A Specialist In A Uniform Repairs A Gas Water Heater Or Boiler

If you have a water heater with a tank, you will often hear it make a hissing sound when it is being filled. This hissing sound is due to the cold water coming in contact with a hot medium.

After using the water heater for an extended period, the water level drops, but when it fills back up, the cold water forms condensation outside the tank.

The condensed droplet rolls down the tank and comes in contact with the hot surface. And considering the large surface area in contact with a hot surface, it quickly evaporates, creating a hissing sound.

In such a case, you do not have to worry about this hissing sound as it is normal and not an indication anything is faulty with your water heater.

4. Sediment Build-Up

Heating Element, Rust And Scale On Boiler Background, Lying On Wooden Table.

Finally, sediments could build up in the tank, which can cause a hissing sound. When sediment build-up is the culprit behind the hissing sound, it is often accompanied by popping noises.

Sediments build up in the water heater tank from minerals in the water source. These sediments settle at the bottom of the tank forming thick layers.

These layers can trap water bubbles which turn to steam in the tank producing the hissing and popping noise you hear.

If you notice your shower water does not make your soap lather as well as it used to, then know sediment build-up is the culprit behind the hissing. Hard water does not make soap lather, so you have to clean up the tank to remove the mineral layer to fix the issue.


As you can see from this guide, if your water heater is hissing, it doesn’t necessarily mean a call for alarm. It would be best if you inspected the noise further to know your next line of action.

Sometimes, you can fix the issue by making a few adjustments to the water heater. Other times, a replacement service is all it takes to fix a hissing water heater.

But if you are unsure of the cause of the hissing noise, contact an expert to service your heater.

Frequently Asked Questions

Why Does My Water Heater Hiss and Spark?

If your water heater is not only hissing but sparking at the same time, it is a sign of a serious issue.

If you are using a natural gas heater, you should quickly turn off the gas supply to the heater and quickly call a professional for assistance.

Is It Normal for Water Heaters To Hiss?

In some cases, it is normal for the water heater to hiss, such as when you refill it with cold water. But if it hisses nonstop, it indicates something is malfunctioning.

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