Navien Tankless Water Heater Loud Banging Noise [Solved]

Tankless water heaters are a great investment since they take up less space and require less maintenance. But if your tankless units make unusual noises, it’s normal to be alarmed. So, why does your Navien tankless water heater make a loud banging noise?

From my years of experience working with different tankless water heaters, I can tell you that the main reasons behind this are:

  • Sediment build-up.
  • Water hammering.
  • Loose installation.
  • Dirty blower fan.
  • Incorrect manifold pressure.
  • And more.

Besides, there are a few other reasons that can cause a banging noise in your Navien water heater. I’ll talk about all these culprits and their solutions in detail in this guide. So, let’s dive in!

I’ll talk about the main reasons why your Navien water heater makes a banging noise or sounds like a jet engine in this section.

01. Sediment Build Up

The number one reason behind your Navien water heater making a loud noise is due to sediment build-up in the water heater. You may think that the water supplied to your heater is pure water. But that’s not the reality.

There are many chemicals or minerals that get inside your water heater with the cold water supply. The most common minerals are Magnesium and Calcium. The amount of sediments that will get inside the water heater depends on the level of water hardness in your area.

sediment build-up in the water heater

If you live in an area where the level of water hardness is high, your water heater will soon be filled with sediments. When that happens, the heat exchanger gets clogged and makes a banging noise.

How To Fix:

Though a clogged heat exchanger is a serious issue, you can easily fix it if it’s not too late. You need to flush the heat exchanger to get the sediments out of the water heater.

Flushing your water heater is an easy process that takes about an hour. You’ll need a flush kit to do this procedure. The kit usually has a recirculation pump, a cleaning solution, and a few hoses.

You can flush the heat exchanger yourself. I’ve compiled a dedicated guide on flushing a Navien heat exchanger. You’ll find everything you need to know about the flushing procedure in that guide. So, check it out.

Ideally, you’ll flush your water heater at least once every year. You may have to do more than that if you live in an area where the water supply has a high hardness level. You may have to do the procedure twice a year in that case.

If you find the need to flush your water heater often, you should install a water softener. It’ll prevent the buildup of sediments by making the water softer. So, you’ll have to flush the heat exchanger less frequently.

02. Water Hammering

Another common reason behind a loud noise coming from your water heater is water hammering. It’s caused when the direction of the water flow is changed or there’s abnormal pressure. The pipes being loose or insufficient space for the condensation can lead to this water hammering issue.

How To Fix:

The simple fix to this issue is to install a water hammer arrestor. You can install it in the cold water supply line that goes to the tankless water heater. Ideally, it should be within 6 feet of the water heater. If you do that, the problem will go away.

water hammer arrestor of navien water heater

03. Loose Installation

The water heater itself and the parts inside the water heater need to be installed tightly. If any of them are loose, the water heater could make a banging or knocking noise.

First, you have to check if the water heater itself is loose. You can do it by inspecting if the water heater vibrates excessively when it’s operational. If it does, you may have just found the culprit.

inspect the navien water heater installation

If the exterior of the water heater doesn’t move much but the movement seems to be coming from the inside, you need to check it too. Take off the front cover of the water heater by removing the four screws. Then, see if you can find the particular part where the noise is coming from.

How To Fix:

If the water heater itself is shaking and the noise is being created due to banging against walls, you can use padding between them. There are some rubber gaskets you can install between the heater and the walls to reduce the noise. Hopefully, the noise will no longer bother you if you do that.

Another option is to install anti-vibration mounts to absorb the shock. But the issue is that you may have to reinstall the water heater in some cases. So, unless the noise is giving you too much of a headache, there’s no need to use this method. Simply installing rubber padding should be enough.

If the noise is coming due to the movement of the internal part of the water heater, you need to tighten it. It could be a simple thing like a flow sensor or another part. When you make the connection tight, the noise should go away and the water heater should work normally again.

04. Dirty Blower Fan

I already talked about how loose parts inside the water heater can lead to a banging noise. The most common internal part that is often the main culprit and makes your Navien water heater sound like a jet engine is the blower fan.

blower fan of navien water heater

It often happens that small insects or months will get inside the fan. Those little things are enough to make the fan lose its balance during operation. As there’s dirt in the way, the heater doesn’t function properly. So, you end up hearing the loud noise.

How To Fix:

The fix is simple – you’d have to clean the fan. It’s located at the top of your water heater. Remove the front panel of the water heater first and locate the fan. You’d have to remove three screws and undo the wiring connection of the fan. Then, you’d be able to pull it out.

You can use compressed air to clean inside the fan and get the dirt out. Be gentle when you clean the fan and make sure you don’t cause any damage to it. When you get the dirt out, reinsert the fan back in its place. Hopefully, the Navien banging noise will go away after that. 

05. Incorrect Ventilation

This one may not be the most common reason behind the banging noise your water heater makes. But I’ve seen it happen a few times. So, you should know about it and check if this is the issue.

navien water heater ventilation

If the air intake vent and exhaust vent are located next to each other, it could be a major issue. The gas from the exhaust will be sucked in by the air intake and the hot air creates a major flutter. So, the entire system would vibrate.

Secondly, there’s also the possibility that something has gotten into them. Things like small twigs, branches, insects, moths, and wasps can get inside them and obstruct the ventilation.

How To Fix:

If you have the intake and exhaust vents located in close proximity to each other, you need to relocate them. You can use different elbows to make sure that they’re pointed in different directions.

Secondly, check for obstructions in both the intake and exhaust vents. If there are any, remove them to get rid of the banging noise. Once you do that, the problem should go away.

06. Incorrect Manifold Pressure

The manifold in your water heater is the component that sends gas to the burner of the water heater from the gas valve. There are three zones in the manifold. Each of them needs the right amount of gas so that the water heater can operate properly.

The manifold pressure may not be correct and cause this issue. You need to check it and see if that’s the case. The manifold may also fail to work properly if there are dust deposits on it.

A failed manifold can even leak gas and cause this issue. It leads to poor combustion and banging noise as well. You can see the error codes E003, E004, and E012 when something is wrong with the manifold.

How To Fix:

If the manifold pressure isn’t at the right level, you need to adjust it. The first possibility is that doing it will solve the problem. However, that may not happen. The noise could still persist.

If the manifold is dirty, clean it as well. But if it’s damaged, you have to replace it. Replacing the manifold can be a tricky thing to do on your own. So, you should take the help of a qualified technician to fix this one.

07. Low Water Pressure

It’s normal to hear a banging noise come from the water heater when the system pressure is low. It’s not the fault of the heater but the water pressure. Ideally, the water pressure should be somewhere between 12-15 PSI.

You need to check the water pressure to determine if this is the issue. Another sign that you’re facing the issue is the formation of air bubbles. The noise actually comes from the bubbles as you hear them pop as they leave the heat exchanger in your water heater.

The noise can also remain for a while even after you turn off the water heater. But it shouldn’t last for more than 10-15 seconds if the banging noise is caused due to this issue.

How To Fix:

First of all, you need to turn off the water heater and the banging noise should go away after a while. For a permanent fix, you’d have to adjust the water pressure to the right level. It has to match the recommended settings of your water heater.

Moreover, flushing the heat exchanger is also recommended. It’ll clean the system and you’ll have an easier time operating the water heater if you do that.

08. Water Flow Issues

If the Navien banging noise increases when you turn on more hot water faucets, it’s likely that there are flow-related issues in the heater. You can test it by using a long screwdriver and pressing the tip of it to the hot water outlet of the water heater.

Make sure the plastic handle is placed to your ear and have someone open a tap. Inspect the different taps in your house using this method. If you hear the roaring or banging noise coming from that area, you’ve found the culprit.

Water flow issues are normally caused when there’s something wrong with the different water sensors or filters in the water heater. A faulty water flow sensor could be the main culprit in this case. Besides, a loose faucet washer will also cause this issue.

flow sensor of navien water heater

How To Fix:

The procedure to solve this problem depends on what caused the trouble. If the faucet washer is to blame, you can easily replace it and the annoying noise will go away. The next thing to check is the flow sensor. If it’s damaged, you’ll have to replace it.

But if it’s a little more complicated and one of the sensors has gone bad, it’ll take more work to replace them. It’s highly likely that you won’t be able to locate or replace the sensors on your own. So, take the help of a qualified technician in that case.

09. Gas Supply Issues

If the noise is coming from the burner area, there’s a strong chance that something is wrong with the gas supply. Turn off the gas supply and see if the noise stops. But don’t do it while there is a demand for hot water. The heat exchanger will get overheated in that case.

gas supply issues of navien water heater

If the noise stops, it’s likely that the gas supply is to blame. The most common culprits in this case are not opening the gas valve all the way or using the gas line of the wrong size.

How To Fix:

Inspect the gas valve and see if it’s only partially opened. It should be completely parallel to the gas lines. If it’s not all the way there, then adjust it and maybe that would solve the issue.

The next item on the itinerary is to check the gas line. If it doesn’t match the one recommended by Navien, that explains the issue. Replace the gas line leading to the water heater with one that’s of the appropriate size. Hopefully, doing these things will help you get rid of the banging noise.


Is it okay if my Navien tankless water heater makes a little noise?

Yes, it’s perfectly normal for a tankless water heater to make a small amount of noise when they’re operational. But it’s not normal if the water heater makes noise when it’s not active or the sound gets too loud.

Can turning off a hot water faucet all of a sound cause water hammering?

When there’s demand for hot water, the water flows through the pipes. As you turn it off, the check valve blocks the pathway and the rushing water bangs in it. So, it creates the water hammering.

What are some signs that you need a water softener in your house?

If the level of hardness in the water in your area is too high, you’ll need a water softener. The signs that you need a water softener are hearing noises from your heater, your skin and hair feels brittle, and and the bathroom floor gets easily dirty.

Do you need to maintain water softeners too?

Yes, all things need maintenance to get the most use of them. You’d have to inspect the salt levels from time to time and replenish them when they get too low. You’d also have to clean it at periodic intervals.


Now, you know all the main reasons why your Navien tankless water heater makes a loud banging noise and how you can fix them. Diagnose each and every problem until you find the root cause behind it.

Hopefully, it’ll be a simple problem that you’ll be able to solve without too much effort. If your Navien water makes a humming noise instead, check out my guide on it. If all goes well, there’ll no longer be any issues with noise after you go through both these and implement the fixes.

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