Hot Water Heater Making Knocking Sounds? (We Have A Fix)

Stacy Randall
by Stacy Randall

A water heater is a lifeline when it comes to being comfortable in your home. If it involves water, then you need a reliable way to heat things when necessary. This is why it is so essential to make sure you take care of your water heater properly.

You’ll commonly hear knocking sounds in your water heater when too much sediment builds up at the bottom of the tank. The severity of the issue depends solely on if the water heater runs on gas or electricity. However, the solution will be the same.

Before diving into fixing the tank, there are a few things you need to know about it. This information includes what powers your tank and what damage sediment can do to the pieces. It will be hard to turn off the water if you do not know how it is powered.

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How Does a Hot Water Heater Work?

A water heater essentially heats the water throughout the house. If the water heater is not working, many daily tasks will become more challenging (and more uncomfortable; ick, cold showers).

Cold water comes in through the dip tube, and either a gas or an electric element heats the water. You can find these elements located inside of the tank. The hot water rises inside the tank and spreads out through the house using the heat-out pipe.

Hot Water Heater Tanks

The water heater tank aims to store hot water that it can later distribute throughout the house. The average tank for a small family is typically 50 to 60 gallons. In contrast, a larger family would do better with an 80-gallon tank.

However, water heater tanks can range from 2.5 gallons to nearly 100 gallons of water. You typically find the larger tanks in public areas such as malls. When you start hearing knocking sounds in your water heater, you likely hear them coming from the tank. However, there is no need to panic.

Although this problem can cause broader issues, it’s relatively easy to fix if you catch it in time. However, even though the steps are simple, be prepared to spend a good majority of the day flushing the tank.

Damage Caused by Sediment Build Up

On a gas water heater, the sediment build-up can cause hot spots on the tank. These hotspots can potentially cause damage to the tank and premature failure. There is no way to repair a failed water heater tank, so this issue would call for replacement.

On an electric water heater, the sediment build-up can cause the lower heating element to fail. Replacing the heating element is much more complicated than flushing the sediment from the tank.

Therefore, it is in your best interest to take care of the build-up before it damages something else. If you promptly handle the situation, it could save you plenty of time and money in the long run.

How To Flush the Sediment Build Up

Before you flush the water heater, ensure that nobody in the home is trying to use the hot water. This includes anybody taking a shower, doing laundry, or washing dishes. Let everyone know you will need to shut down the water heater for a while.

In fact, it would also be a good idea to make sure that everyone has showered and has clean clothes. Flushing sediment build-up can be rather time-consuming.

Tools Needed for You to Complete the Job:

  • A garden hose to drain the water tank
  • Flat-head screwdriver 
  • A large heatproof bucket, if you do not have a drain
  • A towel nearby (just in case)

Step One: Turn Off the Water

If you have an electric water heater, you simply flip the power switch. If you have a gas-powered water heater, turn the thermostat to the “pilot” setting. Leaving the water on will let the water continue to flow and defeat the purpose of draining the tank.

Step Two: Turn Off the Cold Water Valve

For a water heater to transfer hot water through the house, it must first bring in cold water. Cutting off the cold water valve will stop the flow of cold water. If you miss this step, you will have water flow as you are trying to drain the tank.

Step Three: Let the Water Cool Down

The average temperature of a water heater is between 120 and 140 degrees. It is never ideal (or safe) to drain scalding hot water. Ideally, you want to give the water two hours to cool down before draining.

Keep in mind that larger tanks will take more time to cool down, and smaller tanks will take less time. However, two hours should be sufficient for an average-sized tank to cool.

Step Four: Drain the Water

Attach a garden hose to the drain valve on the side of your water heater. Make sure the hose on the valve is tight, or you will end up cleaning up a mess. If the hose is not attached correctly, you’ll end up dealing with a bunch of leaks.

Put the other end of the hose in a drain or a large heatproof bucket. The last thing you need is to flood your home. With that in mind, try to determine if your drain is going to overflow or not.

Step Five: Turn on a Faucet or Two

Turn one or two of the faucets in your home, making sure to use the “hot” setting. This step stops a vacuum from forming in the pipes. Do not be alarmed when there isn’t much water coming out of the tap. Remember, you have turned off the cold water valve. Consequently, no cold water flowing in means there will be no hot water to flow out.

Step Six: Drain the Tank

Use a flat-head screwdriver to turn on the valve slowly. By draining the tank slowly, you can watch for leaks and catch the bucket or drain before it overflows.

If you notice a leak, try tightening the hose onto the valve. If this does not work, you can lay a towel underneath to catch the excess water. If you have to drain the bucket, make sure that you have stopped the water flow first. Otherwise, you’ll end up with a bigger mess on your hands.

Step Seven: Turn the Hot Water Heater On

Once you have finished draining the tank, turn the drain valve off and remove the hose. Then turn the cold water valve and the heating element back on. Pay close attention to your faucets. Once they return to normal flow, you can turn them off.

Note: The water will not be warm. The faucet returning to normal flow is only a sign that the tank is now full. It will take about 30 to 45 minutes for the hot water to circulate through the home again.

It is also essential that you not turn the water heater on while it is empty, or before it gets full. Under no circumstance should you turn the water heater on with no water inside of it. Doing so will result in even more damage, which means even more money to fix it.

Step Eight: Time for a Hot Shower

Now that you have waited for the hot water to circulate, you can finally wash up after a job well done. Nothing beats a hot shower after a hard day’s work.

Reset the Water Heater

If you’re having other issues with your water heater, first locate the thermostat. There will be a red button above the thermostat. When the reset button trips, push the button in to reset it. If the button will not stay in, that may mean that you need to make additional repairs or call for service.

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Related Questions

What is the average lifespan of a water heater?

The average lifespan of a water heater is 6 to 12 years. If you have had the water heater for at least 10 years, it might be getting pretty worn out. Now would be a good time to think about a replacement.  Otherwise, you could end up with a busted water heater and a potential flood in your home. Place a drain pan underneath the water heater to help prevent damage from slow leaks. You can purchase a drain pan for about $25 to $50. That’s a worthwhile investment for the trouble and money it can save you if your water heater starts to leak. 

What if I have no hot water at all?

If you have no hot water at all, chances are your tank has failed. The only option would be to replace it. A brand new water heater tank can cost you anywhere from $360 to $1,000, depending on the size.You could also opt for a tankless water heater, which typically costs more on the front end. This price can vary based on what powers the heater. A gas heater will cost about $3,000, while an electric heater will cost about $1,000. However, tankless water heaters are more efficient than a storage heater. Not only do they leave more space in your home, they will also save you money annually! 

What is more efficient? A gas or electric water heater?

An electric tank heater is typically more efficient, although you should always consider the specific model you plan to purchase. A gas water heater tends to lose some of the heat it produces. This could make it less efficient and cost you more money in the long run. However, gas water heaters are usually cheaper to operate, even though they cost more upfront than electric heaters. Also, certain gas models could be more efficient than certain electric models. Therefore, always weigh all of the factors to decide which is the best fit for you and your home.

Stacy Randall
Stacy Randall

Stacy Randall is a wife, mother, and freelance writer from NOLA that has always had a love for DIY projects, home organization, and making spaces beautiful. Together with her husband, she has been spending the last several years lovingly renovating her grandparent's former home, making it their own and learning a lot about life along the way.

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