Navien Tankless Water Heater Leaking [How To Fix]

A tankless water heater has very little time to heat the water and get it to the desired temperature. If there are any leaks in the system, you won’t get adequate hot water. It can also cause other issues in the heater in the future. So, what causes the Navien tankless water heater leaking problem?

From my personal experience of working on many heaters over the years, I have identified the most common areas from where a Navien water heater leaks. It’s usually the condensate trap, damaged pipe connections, heat exchanger, air separator, and exhaust pipe.

I’ve shared detailed guidelines on how you can fix leaks in each of these areas in this guide. Moreover, there are many additional tips for you to prevent your water heater from leaking so that you don’t face this issue again. So, let’s dive right in!

navien tankless water heater leaking

I’ll talk about the main areas of leaks in Navien tankless water heaters and what causes them. You’ll also learn about the solutions and how you can take corrective actions to fix those issues.

But before getting into them in detail, it’s important that you identify the leak correctly. If you can easily tell where the water is leaking from, then you don’t have to follow the diagnostic process.

You can just look at the area of the leak, and follow the correct procedures and you’re all done. But if you’re not entirely sure about where the leak is coming from, you need to find out the right source of the leak. Otherwise, you’ll take corrective actions that won’t address the main issue and the leak will continue.

How To Find Out Leak Source In Navien Tankless Water Heater?

Sometimes, the leak will be obvious. You won’t have to do anything to find its source. For example, if the water is leaking through the bottom, it will most likely be leaking from the condensate drain or the water supply connections. You don’t have to find the leak source in those cases as it’s apparent.

However, the situation gets much more challenging when the leak is coming from inside the unit. That’s when you need to get more involved in the diagnosis. You can follow these steps to find out the leak source in such cases:

  1. Turn off the water supply and remove the power connection of the water heater at the power outlet.
  2. Remove the screws holding the front panel of the water heater and take out the front panel.
  3. You’ll have eyes on the inside of the water heater and you should be able to see where the water is leaking from in most cases.

Remember that the main sources of leaks when the water heater is leaking from inside are usually the heat exchanger and the air separator. Your Navien tankless water heater could be dripping or leaking heavily depending on the severity of the issue

Keep an eye on these two components as they’ll be the leak sources in most cases. However, if they’re not leaking, it could be another common component in the water heater. You just need to find out what it is called and order a replacement part for that component.

So, now you know how you can identify a leak source correctly. The next step you need to follow is their solutions and implement them to fix the issue. Here are the most common areas of leak according to my own experience along with their fixes: 

01. Navien Tankless Water Heater Leaking From Bottom

When the water heater leaks from the bottom, the leak usually comes from one of these two sources in most cases:

  1. Condensate drain or trap.
  2. Damaged inlet and outlet connections.

I’ll talk about both of them in detail as they’re quite common sources of leaks in a Navien tankless water heater. 

i) Navien Leaking From Condensate Drain

Another common area of a leak in a Navien tankless water heater is from the condensate drain. Look under the water heater and see if there’s a pool of dirty water at the bottom.

condensate drain of navien tankless water heater

If the condensate drain at the bottom of the unit has overflowed along with that, you can tell that that’s the source of the leak. Here are the most common reasons behind it:

ii) Filthy Condensate Drain

It shouldn’t come as a surprise that the condensate drain located at the bottom of your Navien tankless heater becomes dirty with time. As it always gets covered with acidic water or condensate, it can dirty.

The dirt can lead to blockages in the condensate trap and cause the water to leak when there’s too much build-up of condensate.

iii) Loose Navien Condensate Trap O-ring

The O-ring in the Navien condensate trap acts as a sealant to prevent leaks. Unfortunately, it can get loose or wear out over time. In either of these cases, it’s a very common scenario for water to leak from there.

iv) Improper Ventilation

You may think that improper ventilation would never lead to leaks. But that’s where you’d be wrong. The venting plays a key role in the build-up of condensate in your water heater.

Weak venting will often lead to excessive condensate formation. If too much condensate builds up, it will eventually start leaking. You need to inspect the venting and find out if this is the potential issue behind the leak.

Why You Shouldn’t Take Condensate Drain Lightly?

A lot of people make the mistake of thinking that condensate drain is no big deal. But that’s not true at all. There are many issues that could make condensate drain a nightmare for you. Here are the top reasons why you should never avoid a condensate leak:

i) Causes Damage To Property

Condensate drain is a bit more serious and annoying than other leaks as it can damage your property. The water that leaks from the condensate drain is acidic in nature. So, it can easily damage the floor of your house.

Besides, the objects and walls that are near the heater can also get damaged because of it. As the water is acidic, it can also lead to corrosion in the pipes that are connected to it. The worst-case scenario is that it will lead to corrosion in the heat exchanger.

ii) Reduces Efficiency Of The Heater

Properly draining condensate is necessary for the heater to achieve maximum operational efficiency. If that is not maintained, the heater won’t be above to give it optimal performance. That means you’ll have to wait longer to get hot water when you need it.

iii) Causes Damage To Living Beings

Normally, adults won’t have such a big problem with acidic water in the short run. But it can be harmful for children and pets if they’re exposed to it even for a little while.

To make matters worse, even adults may develop respiratory issues if they inhale the acidic condensate over a long period. So, if overlooked, this issue can cause health problems in both children and adults.

How To Fix:

As there are many potential causes that could lead to leaks from the condensate drain, the fix depends on the issue. It’s important that you identify what’s causing the leak and take appropriate action.

If the source of the leak is a dirty condensate trap, you have to clean it. If it’s damaged or cracked, your only option is to replace it in that case. Make sure to clean the condensate trap as often as possible to prevent this problem.

A damaged O-ring can also cause this issue. If that’s what happened in your case, you need to replace it with a new one. Get a new O-ring of the correct size and install it. Make sure you apply lubricant so that the installation goes smoothly and it can do its job properly.

If there’s excessive condensate, the venting system is to be blamed. Inspect all the venting connections properly and tighten all the weak connections. Make sure that none of the intake pipes or exhaust pipes are obstructed to ensure smooth operation of the water heater.

Damaged Inlet & Outlet Connections

There’s a saying that goes something like your plumbing is only as strong as your weakest fitting. Your Navien tankless water heater is connected to inlet and outlet pipes.

pipe connections of navien tankless water heater

Cold water comes through the inlet pipe and makes its way to the heater. The heat exchanger heats the water and sends the hot water through the outlet pipe. Everything needs to be in order for that process to go smoothly. However, that process is commonly interrupted in two ways.

Firstly, the connections of the pipes may not be fully secure. If they are weak, it’s common for water to leak through them. You’ll be able to see if this is the issue by taking a look at the areas of connection.

Secondly, the pipe connections could get corroded over time. In that case, the connection will also be weak and lead to leaks. If something gets caught up in the pipes, that can also interrupt the flow of water, build up pressure, and lead to water leaks.

How To Fix:

If the reason behind this issue is weak fittings, you can easily correct it. All you have to do is make sure that the connections are tight. Turn off the power to the water heater as well as the cold and hot water supply.

Then, you can tighten the connections. If you don’t know how to do it, you can consult an expert to make sure that this issue doesn’t occur again. If the pipes are corroded or something is obstructing the flow of water, it’s a good idea to replace them altogether. Hopefully, that’ll fix your water heater leaking issue.

Another common area of leak for a Navien tankless water heater is inside the unit. The leaks occur mainly in the heat exchanger or the air separator in most cases. I’ll discuss both of them in detail as they’re equally important.

i) Navien Leaking Heat Exchanger

Leaks from the heat exchanger are pretty unfortunate. The sad news is that they are also quite common. The main reason why heat exchangers leak is due to a lack of maintenance from owners.

heat exchanger of navien tankless water heater

Most American households have a hard water supply. That means the water has many minerals in it. When they pass through the heat exchanger, some minerals settle in the heat exchanger and pile up on them. That leads to scalde build-up and the heat exchanger can creak and develop leaks.

Then, why I am blaming it on the owners and not the American water system? Because, as an owner, one needs to do these things about the operation of the heater. Even if anyone looked at the manual of the heater, the importance of flushing the heat exchanger is stated there.

Flushing essentially removes the sediments from the heat exchanger and prevents it from getting cracked. So, owners need to flush the heat exchanger so that it can work properly in the long run.

However, if you’ve ignored that and it has been going on for a long time, you may have reached a point of no return. There’s no quick fix when the heat exchanger has cracked.

How To Fix:

If you haven’t flushed your heat exchanger at proper intervals and it is cracked, your heater could be leaking from that area. Unfortunately, heat exchangers can’t be repaired.

So, your only option is to replace the heat exchanger when it has failed. The process is to disassemble the unit, remove the old heat exchanger, install the new one, and put it all back together.

It may sound simple but it’s not that easy. You need to have a good knowledge of working on heaters if you want to pull it off yourself. I’ve broken down the steps to replace the heat exchanger in my heat exchanger fixing guide. Check it out for detailed instructions on it.

However, if you don’t have any expertise in working on heaters, you should hire a qualified technician for this job. Once you replace the faulty heat exchanger, make sure you take good care of it and flush it at regular intervals. Otherwise, the same problem will reappear again.

ii) Damaged Air Separator

When the leak is coming from inside the unit, it’s natural to get worried. Your first instinct could be that the water is leaking from the heat exchanger. But that’s not always the case.

The air separator inside the unit could be the actual cause of the leak. Take a look at the image below to get an idea of what the air separator looks like.

air separator of navien tankless water heater

The correct diagnosis is extremely important for you to fix the issue that’s causing trouble. If you thought the heat exchanger was leaking and replaced it without consulting anyone, you’d wasted a lot of time, energy, and resources.

But you’re much better off taking the time to see where the leaking is coming from. Granted, it’s also common for the heat exchanger to leak. But if you’re lucky, the heat exchanger could be okay and it could be from the air separator. Either way, your diagnosis should be spot on.

How To Fix:

You’d have to replace the air separator if it’s damaged. The good news is that it’s an incredibly easy process to get it done. You won’t need any outside help for this job. Follow these steps to replace the air separator in your Navien tankless water heater:

  1. Turn off the power to the water heater and unplug it from the outlet.
  2. Remove the front cover of the water heater after taking off the screws that hold it in place.
  3. Locate the air separator from the picture shown to you above. You should already know how it looks if you’ve done the diagnosis properly.
  4. Use a pair of pliers to loosen the old air separator and remove it.
  5. Put the new air separator in place of the old one and tighten it with the pliers.
  6. Attach the front cover of the water heater and turn the power supply to the unit back on again.

Replacing the air separator is much easier and better than replacing the heat exchanger. A heat exchanger will leave a massive hole in your wallet but an air separator is inexpensive. It’ll only be around $15 – $25 depending on where you live. Hopefully, replacing it will stop the leak in your water heater.

Besides, leaking at the bottom or inside the unit, Navien water heaters can also leak from the top. The air intake and exhaust pipes are connected at the top of the water heater.

exhaust connection of navien tankless water heater

It’s much more common for water to leak through the exhaust as it deals with more materials like fumes. On the other hand, the air intake is only responsible for supplying air to the water heater.

As the exhaust pipe deals with fumes, it can get corroded over time. If this is the source of the leak in your water heater, I bet that the exhaust pipe is corroded and looks dirty. So, there are cracks in them and that’s where the water is leaking from.

Another possibility is that the seal that’s between the exhaust pipe and the heater could be damaged. If that happens, the water could be leaking from there as well. There’s also the chance that both of them have gone bad together and that’s causing the leak.

How To Fix:

The solution is obvious – if the exhaust pipe is damaged and causing the leak, you’ll have to replace it. The same goes for the seal. If it’s damaged, it also has to be replaced. The process is straightforward and it won’t take a lot of work to fix this issue.

What Are Some Other Reasons Why Your Tankless Water Heater Leaks?

Now you know about the most common sources of leaks. Hard water is the biggest reason that leads to leaks in the Navien tankless water heaters. You should know all about it in detail as it was discussed in the section where I explained heat exchanger leaks.

Apart from that, there are two other common reasons why your water heater could be leaking. You should know about them and follow the corrective mentions mentioned to make sure your water heater doesn’t leak. 

i) High Water Pressure

Another common reason why your water heater could leak is due to excessive water pressure. If the water pressure is higher than what it’s supposed to be as per the city regulations, it could be an issue.

All cities have certain regulations when it comes to the water pressure. For example, the household water pressure in LA County shouldn’t exceed 80 PSI. You can simply look up the recommended pressure for your state and check it against the pressure regulator.

If you don’t have a pressure regulator, you should contact a plumber or contact Navien support to get one installed. It will help you diagnose whether this is the issue as you’ll be able to check the water pressure by taking a look at it.

When the water pressure is too high, it can damage the different components in a water heater. Eventually, they can get damaged to the extent that they get cracked and water can leak through them.

How To Fix:

Installing a water pressure regulator can be a solution in and of its own along with being a diagnosis. That’s because you can adjust the water pressure in your house by adjusting the pressure regulator.

adjusting the pressure regulator of navien tankless water heater

Once you know the right water pressure for your house, you need to match it with the reading in your pressure regulator. It’s likely that you’ll have to decrease the water pressure. So, turn the screw to the left to do that.

In case this isn’t the issue, don’t try to play it extra safe and reduce the water pressure to a ridiculously low level. If you set a water pressure that’s too low, it’ll take a long time to heat the water as less of it will flow through the heater. 

If the water pressure is already too low, turn the regulator to the right to increase the pressure. Just maintain the city regulations when it comes to water pressure and you’ll be fine. There’s no need to be fancy and increase or decrease it beyond what’s right for your house.

Another option you can use to prevent any issues related to water pressure is installing an expansion tank. It’s normal for the water to expand due to heat and that can create a lot of extra pressure.

An expansion tank will fight against that and prevent any damage to the water heater. It’s also a great tool used in many households to make sure that no unwanted water pressure spikes take place.

ii) Heater Is Old

Navien tankless water heaters are one of the most reliable heater brands out there. But even the better ones can only run for so long. If you feel like your water heater is leaking from multiple areas, the simple reason behind it is that your heater is too old.

As the heater ages, certain parts will wear out.  The heater will also lose efficiency over time and you’ll notice the effect on your energy bills. As the parts get damaged or worn out, they can eventually lead to leaks.

How To Fix:

When dealing with this situation, you should honestly consider even if it’s worth it to try and repair the heater. It all depends on the source of the leak and which part is leaking.

The most important part of the heater is the heat exchanger. If it’s corroded or damaged, that’s a big issue. In that case, you should no longer replace the heat exchanger and instead, opt for a new heater.

But if it’s other parts like a condensate drain or some vent connections or corroded pipes, you should fix them. You may get a few good additional years out of your water heater if you do that.

The reason I don’t recommend changing the heat exchanger in an old heater is because it’s expensive. Moreover, it won’t be a good solution as the other parts in the heater won’t be in topmost condition.

So, the heat exchanger will get corroded a lot sooner as the supporting parts are also most likely corroded. That means you won’t get a good return on your investment if you replace the heat exchanger. So, you’re much better off replacing the heater altogether.

How To Prevent Navien Tankless Water Heater From Leaking?

There are many steps you can take to ensure that your water heater has minimal chances of leaking. This isn’t a hard job at all and will increase the chances of your heater lasting a long period. Here are some key things you can do to prevent any water leaks in your water heater:

i) Flush Your Water Heater

Hard water supply is the number one cause of water leaks in water heaters. It’s very common in most American households. The build-up of magnesium, calcium, and other minerals can end up damaging the heat exchanger.

Once you have a cracked heat exchanger, it will start leaking. Replacing it will also be an expensive endeavor. But you can easily solve this issue by flushing the heat exchanger.

Flushing your water heater means running a descaling solution through the heat exchanger. It removes the sediments that are already there and also reduces the build-up of more minerals.

flushing the heat exchanger of navien tankless water heater

Usually, Navien tankless heaters need to be flushed once or twice a year depending on the level of hard water. It’s a simple process. All you’ll need is a flushing kit and you can do it on your own.

Although the process is lengthy and can take some time to complete, the steps are really simple. I have a detailed guide on flushing a Navien tankless water heater where I talk about the ins and outs of this topic. Feel free to check it out to know all about flushing the heat exchanger.

Keep in mind that leaving the scale in your heat exchanger for too long is what damages it and you are left with no other option but to replace it. So, flush your water heater at the right intervals to prevent this issue.

ii) Set Up Water Filtration

As hard water supply is the leading cause of leaks in water heaters, reducing the hardness of the water heater will go a long way in preventing leaks. If you can set up a good water filtration system, the hardness of the water will be reduced. So, it would take a lot longer to build up scale in the heat exchanger.

water filtration

That means you can get away with flushing your heat exchanger at longer intervals if the filtration system does a good job. There are many options you can choose from for the right filtration system for your tankless water heater. 

However, using a water softener is by far the most popular and convenient choice. It’s a great investment as a water softener will reduce the hardness of the water at the very root. It’s usually installed near the main water supply line of your house to soften the water.

Installing a water softener will not only reduce the hardness of the water going to the water heater but to your entire house. So, the water will feel smoother and you’ll even have an easier time doing other household tasks that involve using water.

iii) Installing An Expansion Tank

After hard water supply, extreme water pressure is another common reason for leaks in tankless water heaters. When the water pressure gets too high, certain parts of the water heater won’t have the capacity to handle it. So, it’ll get cracked and the water will leak through it.

expansion tank of navien tankless water heater

One of the most effective ways to ensure that there is no high water pressure issue is to install an expansion tank. You can install it before the water goes to the tankless water heater. If the pressure is regulated, there will be no high-pressure issue and your water heater will remain safe.

iv) Ensuring Correct Installation

Even if you have top-notch products, you need to have the ability to use them correctly to get the most out of them. The same goes for Navien tankless water heaters. Though they are durable and of great quality, not installing them correctly can often cause leaks.

proper installation of expansion tank of navien tankless water heater

Loose fittings are one of the main areas where new installers make a mistake and wreak havoc on the system. One weak fitting in the plumbing lines can mess up the whole performance of your water heater and cause leaks. So, you have to make sure that all the fittings are nice and tight.

Is It Okay To Ignore Leaks In Navien Tankless Water Heaters?

When it comes to tankless water heaters, leaks should never be ignored. Especially, if the source of the leak is inside the unit. If water is leaking from inside the unit, it can damage the other components in the water heater.

For example, if the heat exchanger is leaking, the water can also get into the control board and damage it. If that happens, your entire water heater will go bad and you’ll have no option to replace it.

That’s why the first thing you should do when water is leaking from your water heater is to stop using it. Then, identify the source of the leak as mentioned in this guide, and take action to fix it. Don’t think that it’s good to use your heater in this condition as you can end up destroying it.

You may also see a different type of leak from your Navien tankless water heater. It can be brownish in color and can also seem to be a bit oily. It’s possible that it’s just condensate you’re looking at.

The other thing that could have happened was that the exhaust was leaking back into the system. No matter what the leak is, the fundamental fixes are still the same. Whether it’s just water or the oily substance, it won’t change much for you when it comes to implementing the fixes.

brownish leaks in of navien tankless water heater

You already know that the most common sources of leaks are the heat exchanger, condensate trap, air separator, exhaust pipe, etc. These are still the areas that you should check to find out where the leak is coming from.

Once you know the leak source, you can easily fix it. Follow the solution section for the problem you’ve identified and that’s all you’ll have to do. Hopefully, applying the solution will fix the leaking issue in your water heater and you’ll get sufficient hot water.


Is water leaking from the condensate drain dangerous?

Condensate coming from the water heater is a normal procedure for a Navien tankless water heater. It’s usually harmless to adults but as it contains acidic waters, it’s not safe for pets and children.

Should you install a Navien tankless water heater yourself?

Installing the Navien tankless water heater on your own can lead to mistakes which can eventually lead to leaks and even damage to the water heater. So, I recommend getting it installed by a professional HVAC expert.

What is the main job of a water pressure regulator?

A pressure regulator attaches to the main water line of your house. It ensures that the water coming into your house has a safe pressure level.

Should you install any safety device to protect your water heater?

If your plumber recommends using any device, you should ask about the specific reason why it’s important. You can also ask other people in your neighborhood if they have similar devices installed. If you get positive feedback on it, you can get the safety device installed.


Now you know the main reasons behind the Navien tankless water heater leaking and how you can fix them. Look at the common potential problem areas one by one until you’re 100% sure where the leak is coming from.

Once you’ve identified the leak, it’s a simple process of applying some fixes to stop the leak. Hopefully, you’ll be able to do that easily after following this guide. If your Navien water heater is making a loud banging noise, check out my guide to learn how you can solve it.

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