Hidden Plumbing Problems: What to Look for

What Can Cause A Tankless Heater To Make Loud Banging Noises When You're Using It?

2 October 2020

Herbert Chambers

While tankless water heaters can be a bit loud while they're in operation, they should never make banging noises. If you can hear your water heater rumbling from the other side of the house, it definitely deserves your attention. Loud bangs can be caused by mineral buildup, air bubbles, or high water pressure in your home. Mineral buildup and high water pressure need to be addressed as soon as possible since they can damage your water heater. To learn more about the possible causes behind your water heater's banging sounds and how they can be fixed, read on.

Mineral Buildup

The most common reason for a tankless water heater to make a loud banging noise is an excessive mineral buildup in the pipes. When dissolved minerals settle in a pipe, they often trap a tiny amount of water underneath.

Tankless water heaters get very hot—they need to be hot enough to quickly heat water as it moves through the heat exchanger. When the water's trapped underneath the mineral scale, it has nowhere to go. Eventually, the high temperatures will cause the trapped water to boil and transform into steam, causing a loud bang as it expands.

The solution to this problem is to have your heater de-scaled by a tankless water heater repair service. You need to have this done annually, and you will need to do it more often if your home has extremely hard water. De-scaling your tankless water heater to remove mineral buildup will prevent it from making banging noises and also improve its ability to heat water efficiently.

Air Bubbles in the Heat Exchanger

If there's an air bubble inside your heat exchanger, it will expand as temperatures rise. When the air bubble arrives at your water heater's outlet pipe and is no longer being heated, it will rapidly collapse and cause a loud bang.

This problem typically resolves on its own. It's common after you have maintenance performed on your tankless water heater. Ideally, air should be bled from the pipes after you or a plumber has worked on them. However, it's often impossible to remove all of the air. Small air bubbles that remain can later cause loud bangs once you use your tankless water heater again. Once all the air is gone, the banging will stop.

High Water Pressure

Finally, high water pressure can cause loud banging noises due to the water hammer effect. Although this problem isn't unique to tankless water heaters, it's frequently encountered with them due to the small diameter of the pipes in the heat exchanger.

The pipes inside a tankless water heater's heat exchanger snake around the inside whole unit in order to give the heating element enough time to warm the water. If the water pressure of your intake pipe is extremely high, the water will create shockwaves throughout your pipes whenever it changes directions quickly. The shockwaves will create loud banging noises throughout your pipes.

The solution to this problem is to have a plumber install a pressure regulator valve on the tankless water heater's cold water intake pipe. Reducing the pressure will prevent water hammer and also help prevent your tankless water heater from being damaged by extremely high water pressures.

What should you do if your water heater keeps making loud banging noises? If they stop eventually and don't return, it was likely due to air bubbles in your water heater, which can safely be ignored. Otherwise, you'll need to call a tankless water heater repair service to have your water heater inspected. If it needs to be de-scaled or if a pressure regulator needs to be installed, it's a good idea to have it done quickly—neglecting to fix mineral buildup or high water pressure can lead to damage to your unit.

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