4 Common Reasons Why Water Heater is Making a Hissing Noise

There are four main reasons why your water heater could be making a hissing sound, and those are:

  1. High water temperature
  2. Build-up of sediments
  3. Leaks or fractures in the tank
  4. Condensation

Most of these problems are not severe and shouldn’t cause immediate concerns. I’ll go over the different reasons in more detail below and let you know if you should be worried and whether or not you need to contact a professional for more help.

Why Your Water Heater is Making a Hissing Sound

#1. High water temperature

If the water heater output temperature has been set too high (140 degrees or higher), the T&P (temperature and pressure) valve will open to offset the extra internal pressure created. In return, your water heater will make a hissing sound. You should note that the level of pressure build-up is equivalent to the degree of water temperature.

The T&P valve works automatically. It will open when the water temperature hits a dangerous level to expel steam and, in return, release the generated extra internal pressure. This level of heat differs from heater to heater.


The best way to handle this problem is by lowing the temperature in the tank to around 120 degrees. Once a T&P valve gets opened, the valve is no longer useful and should be replaced. For this, you should seek the advice and service of a professional.

#2. Build-up of sediments

As you heat water, dissolved minerals such as calcium and magnesium crystallize over time and settle at the bottom of the heater. Regular build-up leads to the formation of sediments. The extra accumulation of sediment is more common in areas with hard water.

How is this connected to your heater’s hissing sound? As sediment forms, water gets trapped between the layers of the sediments. As the water in the tanks begins to heat, the trapped water found in between the layers gets extremely hot and begins to boil, causing it to evaporate into steam, which could produce a hissing or sizzling sound.


The only way to correct this problem is by flushing your water heater to remove the sediment build-up at the bottom of the tank. Removing sediment from the water tank is something that you can do yourself, or if you feel more comfortable, you can have a professional do for you.

The steps are relatively simple to follow. Here is an excellent video on Youtube that can help walk you through the entire process.

#3. Leaks or fractures in the tank

Your water heater will make a hissing sound if there are leaks or fractures present in the tank. When there is a leak, water will escape during heating and hit hot surfaces and, in return, produce a hissing sound. Water heater leaks originate from a variety of situations. First, it might be as a result of a loose valve that requires tightening. But often, it could be caused by a corroded tank. In this case, the entire water heater would have to be replaced with a new one.

If you can hear the hissing sound without having drawn a large amount of hot water, your tank probably has a small leak in it someplace. Large puddles of water settling underneath the tank will indicate it is a leak and needs to be addressed right away before the crack becomes worse and causes property damage.  

While you wait for help to arrive, you should turn off the water supply to the heater and switch your dial to vacation or pilot. Proceed to dry the water around the tank as much as possible and check for leakages.


Contact a professional once you realize that your water tank is leaking. You can not repair a leaking water tank; the only way to fix this problem is by replacing the entire water heater.  Remember, if you wait, the leak or fracture might get bigger and lead to the water tank bursting, so as soon as you notice a leak, you should seek immediate help.

#4. Condensation

Condensation is a common cause for a water heater to make a hissing sound. Condensation occurs when cold water fills up the water heater tank, causing small puddles of condensation to build upon the outside of the water tank. With time, the pooled water will run down, and when it comes in contact with hot parts of the water heater, you may hear a hissing sound.


A common reason for condensation to form could be because the water heater is undersized for what your households’ hot water needs are.  You might need to think about installing a larger water heater or looking for ways to limit the amount of hot water usage in the home.

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