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Water Heater Hissing? Do This Immediately!

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

If you have a water heater in your home, you probably rely on it for a lot of basic, everyday tasks, such as showering or washing dishes. 

So, understandably, if your water heater starts making a hissing noise, you might be concerned that it’s damaged or maybe even dangerous to you and your family. 

It’s true that hissing sounds from your water heater (see also ‘Water Heater Parts – Get To Know Your Heater’) sometimes indicate that something is seriously wrong, and in these situations, you’ll want to call a professional as soon as you can.

However, there are also some less concerning reasons why your water heater (see also ‘Should You Invest In Water Heater Booster’) might be hissing, so before you panic, take a moment to read this article and figure out whether this is a problem you can rectify yourself. 

Today’s guide will cover all the main reasons for water heaters hissing and what you should do in each case.

We will also make clear which cases of hissing water heaters need to be dealt with by a professional before answering some of your most-asked questions about water heaters. 

Reasons Your Water Heater Is Hissing 

There are a few potential reasons for that hissing noise coming from your water heater.

Before you spend money on bringing a professional out to your home, it’s a good idea to try and determine the cause yourself. 

Here are the 4 most common reasons for water heaters hissing: 

Overheating Water 

Sometimes, people assume that the hissing noise from their water heater is caused by the heater itself, but this is not always the case.

In fact, a common cause of hissing sounds emanating from a water heater is the pressure and temperature valve. 

More often than not, if the pressure or temperature valve in your water heater is making a hissing noise, it’s because the water is overheating. 

The pressure valve in your water heater is there to prevent the tank from exploding (see also ‘Can Your Water Heater Explode?’) when temperatures or water pressure get too high.

If the water coming out of the tank is too hot, the temperature valve will activate, releasing some of the built-up pressure and producing a hissing sound as a result. 

If you suspect that the hissing noise from your water heater is due to overheating, you should first check the temperature settings on your heater.

If the temperature reads over 140 degrees, you should lower it by 20 degrees and see if the noises subside.

Don’t lower the temperature further than this, though – temperatures lower than 120 degrees can cause bacteria to build up in your water heater. 

Sediment Build-Up

If the hissing noise you have noticed coming from your heater is also accompanied by a range of other sounds (popping, for example), you could be dealing with a build-up of sediment in your water heater. 

The most likely cause of a sediment build-up in a water heater is hard water.

Hard water is water that contains an excess of calcium and other minerals.

An easy way to tell if you have hard water is if you struggle to build up a lather with soap when you wash your hands. 

Minerals in the hard water collect at the bottom of your water heater, accumulating over time, and eventually impairing its functionality.

The hissing noise happens because the sediment layer traps water bubbles, which then turn into steam and make the hissing and popping noises you are hearing. 

Unfortunately, a sediment build-up in your water heater is something you will need to consult a professional about.

They will inspect the water heater and decide whether the sediment can be flushed out or whether the heater needs to be replaced altogether. 


Most of the time, a hissing water heater is a sign that something is wrong, but if the noise is only happening at specific times and after certain types of water usage, it might actually be nothing to worry about. 

Water heaters that have tanks sometimes hiss when water is being pumped into them.

If you’ve just had a long, hot shower, your water heater itself will also be hot from heating up all that water. The water coming into the tank, however, is cold.

When the cold water is introduced to the hot water tank, condensation is created.

As this condensation comes into contact with the hot surface of the tank, it might make a hissing sound. 

With that being sound, if this hissing happens every single time you use hot water or is very excessive, it may indicate that you should make some changes to your water heater.

One common cause of excessive hissing after hot water use is that your tank is too small.

Larger water heaters can accommodate more hot water usage and won’t need to be refilled so frequently, resulting in less hissing. 

A lot of hissing from condensation could also indicate that your water supply is too cold.

The colder the water coming into the tank, the more likely it will be to produce condensation when it enters a hot tank. 

Leaking Water Tank

Leaking Water Tank

Random hissing from your water heater that doesn’t seem to come at specific times could be a sign that the tank in your water heater is leaking. 

If water leaks out of your water tank, it may cause condensation in the same way as we described above: cold water touching a hot tank.

However, condensation hissing because of a leak is much more problematic. 

In addition to the hissing, you may notice that there is excess water or moisture around your water heater.

You may even see it dripping down and pooling underneath the heater, which is the most obvious sign of a leak. This is most likely if your water heater is old. 

If you think that the tank in your water heater is leaking, you should contact a professional as soon as possible. If not addressed, the problem can get worse, leading to more wasted water. Even worse, your heater could eventually burst, which is a dangerous situation. 

Should You Contact A Professional? 

Whether you need to contact a professional about your hissing water heater depends on the severity of the hissing, any accompanying signs of damage, and the time that the hissing occurs. 

If, for example, your water heater is hissing only after you use a large amount of hot water and there are no other apparent issues, you may not need professional intervention – although, if you’re using a small water heater, you might want to consider replacing it with a larger one to minimize the hissing that happens as the tank refills. 

Aside from this, though, we generally recommend getting in touch with a professional if your water heater is hissing.

Most of the time, this is not a normal occurrence, and even if there doesn’t seem to be anything else wrong with the heater, hissing can be a sign of an invisible, underlying issue.

A professional will be able to conduct a thorough inspection and decide whether further action is needed. 

If you ignore the hissing from your water heater, you risk allowing the problem to get worse.

This could, at best, result in a large bill, but at worst, your water heater could sustain significant and dangerous damage. 

Frequently Asked Questions 

Is It Normal For Water Heaters To Hiss? 

No, it’s not normal to hear hissing from your water heater for the most part.

Hissing can be caused by condensation, which may not be a cause for concern, but if condensation-related hissing after water usage is happening often, it’s worth thinking about whether you need a bigger water heater. 

Generally speaking, if your water heater is hissing, you should assume that there is something wrong and speak to a professional. 

Can A Water Heater Explode?

Water heaters can and do explode. This is why it’s so important to be vigilant for signs that your heater isn’t functioning correctly.

One cause of hissing from a water heater is that the pressure is too high due to overheating, which is a leading cause of water heater explosions.

You may also be at risk of an explosion if your heater is leaking or if you can smell gas, so treat these signs seriously and call a professional. 

Why Is My Hissing Water Heater Producing Sparks?

Hissing accompanied by sparks is a very serious problem, especially if your water heater runs on gas.

If gas is escaping from your water heater, it could react with the sparks, causing a dangerous explosion.

As soon as your water heater starts producing sparks, whether it is also hissing or not, you should evacuate your home and call your gas provider.

If the sparks have started a fire, you should call emergency services. 

How Do I Fix A Hissing Water Heater?

Sometimes, you will be able to fix a hissing water heater yourself by adjusting the temperature.

However, most of the time, you will need to leave the repairs to a professional.

This is because your heater may need flushing or replacing, and both of these tasks have to be carried out by someone with the relevant qualifications. 

Final Thoughts 

A hissing water heater can be alarming, but you shouldn’t panic. The cause can be as simple as condensation or high water temperatures.

However, the root of the issue could also be excess pressure or water and gas leaks, both of which can eventually lead to explosions. 

If you have tried adjusting the temperature of your water heater (see also ‘Water Heater Smells Like Burning’) and the hissing or sizzling sound has not resolved, you should call a professional.

It’s always better to be safe than sorry in these situations.

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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