Tankless water heaters are an increasingly popular investment because they consume less energy and are more compact than tank water heaters. Another advantage is their relatively low volume level compared to their tanked counterparts. So it can be alarming if your tankless water heater suddenly starts creating a racket.

This May Also Interest You: How to Flush Your Tankless Water Heater: A 7-Step Guide

If you hear your tankless water heater making a banging noise, it can be concerning, but this isn't necessarily a sign it needs a repair. Here’s an outline of the possible causes and solutions.

Why Is My Tankless Water Heater Making a Banging Noise?

Noise in a tankless water heater is normal when the water is heating up. If the noise is happening at times of low use, like nighttime, it’s probably time to take a closer look.

The most common cause of knocking or banging noise is sediment buildup. Flushing your system regularly is important, especially in areas with hard water. (For a guide, check out the related link above.) Sediment reduces the efficiency and life expectancy of the water heater on top of causing an unpleasant sound.

Loud noise and vibration may also be caused by water hammering, which is when there is a sudden change in the direction of the water flow. This may be caused by loose pipes or insufficient space for condensate. These problems should be fixed by a professional.

Another possible cause of the noise is loose or dirty parts in the unit. This will cause humming noises in the system and can usually be fixed with an easy repair or cleaning.

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• What’s the Deal With Self-Cleaning Water Heaters?
• How to Turn Off Your Water Heater — and When It May Come Up

How Do I Stop My Tankless Water Heater From Making Noise?

If you hear a banging or knocking sound, the first step is to flush your water heater. You can buy a kit specifically designed for the task, or call a professional if you don’t want to do it yourself. You may need to do this twice to flush out larger amounts of sediment. Make sure to repeat this process at least once a year to avoid further problems.

If this doesn't solve the problem, you can try further troubleshooting. Look for loose fittings and pipes and check that no parts — such as valves or flow sensors — have a buildup of dirt.

Should I Call a Plumber?

If you’ve tried the fixes above and your water heater is still making noise, it's time to call a plumber. Although tasks like replacing parts or cleaning a dirty flow sensor can be carried out by the homeowner, you should call a professional if you aren't experienced in plumbing repairs. Tankless water heaters can last a long time if correctly maintained, so work is best carried out with care.

A plumber can install a check valve, which prevents cold water from flowing back into the hot water supply. They can also ensure the system has been flushed completely or check for loose parts that you couldn't detect. It's important to carry out repairs quickly; a damaged water system can cause further problems, such as flooding, in your home.