Navien Tankless Water Heater Exhaust Smells Like Gas [Fixed]

If you have a water heater that smells like gas, it could be a serious problem. You may have noticed a gas smell coming from the exhaust in your heater. So, what causes the Navein tankless water heater exhaust smells like gas issue?

I’ve identified five common reasons that make tankless heaters smell like gas from my experience of working on heaters. Over the years, I’ve found these reasons to be the common culprits behind this problem:

  • Leaky exhaust vent gasket.
  • Poor combustion.
  • Venting issue.
  • Loose glass gauge around the heat exchanger.
  • Leaky gas line.

Keep on reading to find out more about these issues and their fixes in detail. So, let’s dive in!

navien tankless water heater exhaust smells like gas

Is It Normal Or Dangerous To Smell Gas From Your Navien Tankless Water Heater?

You may immediately freak out whenever you notice a gas smell coming out of your heater. And that’s a considerable reaction because tankless water heaters are supposed to have sealed combustion chambers. Ideally, you should never smell gas from your tankless water heater.

However, life is less than ideal. Not smelling any gas sounds good in theory but that’s not how it works in real life. You’ll normally notice a raw gas smell coming from the heater at times during ignition.

If the smell goes away after a while, I wouldn’t make a big deal out of it. There’s no need to panic if that happens to you. It’s normal for tankless water heaters like Navien to discard some unburnt natural gas through the exhaust during ignition. As heaters are designed to ignite quickly, they naturally crack the gas valve open and get rid of some of the gas to get a good burn.

However, it’s only okay to smell gas during the ignition phase. It should not last longer than a few seconds if you keep the unit running. If the smell still persists, then there’s an issue with your heater. Don’t worry, I’ll talk about the potential problems and fixes. Keep on reading to find out all about it.

I’ll talk about the most common reasons why your tankless water heater smells like gas along with the right fixes in this section.

01. Leaky Exhaust Vent Gasket

If your Navien tankless water heater seems to be leaking gas, you need to be thorough with your inspection. Take off the front cover and check the area around the heater.

There will most likely be a build-up of oily yellowish substances. I can tell you that because I’ve faced and fixed this issue myself. The two areas you should check are the bottom of the heat exchanger and just below the exhaust pipe.

unwanted substances of navien tankless water heater

If you see that substance right under the exhaust, there’s a strong likelihood that the gasket has come loose. Because it’s loose, it’s no longer able to get rid of the exhaust gases properly.

That’s why some of the exhaust gas remains in the heater and your exhaust smells like gas to you. If you’re still confused about which gasket I am talking about, here’s a picture to help you out:

How To Fix:

The yellowish substance represents the build-up of carbon monoxide. As it can be a severe issue, you need to fix it as soon as possible. You’ll have to change the exhaust collar vent to fix this problem.

When installing the collar vent, make sure that the exhaust vent pipe is connected directly to the collar. It’ll minimize the movement of air within the heater and will prevent the build-up of gases in the long run.

The great news is that Navein will send you the replacement part for free if your unit is under warranty. The caveat is that you’ll have to get a technician to be on the phone with them. That’s because they only send parts after they talk with a professional in this field.

02. Poor Combustion

If you notice the gas smell throughout the entire burning cycle, poor combustion could be the main culprit here. However, it can be hard to test this issue without the right equipment.

You’ll need a dual port manometer to check the gas pressure and a combustion analyzer to inspect the combustion. As it’s highly unlikely that you’ll have any of these tools on your own, you’d have to call a qualified technician for help.

checking gas pressure with the manometer of navien tankless water heater

Pro Tip: If you suspect this could be the issue, ask the technician if they have both these tools. Many of them would have the manometer but not the combustion analyzer. So, make sure you call the right person and only ask someone to come who has both these tools.

How To Fix:

There can be many reasons behind poor combustion. As you’ll require a technician for inspection, he’ll also guide you on the right steps to fix the issue. Based on my experience, the most common fixes are usually a basic tune-up along with combustion tuning.

Sometimes, the flame rods will also have to be cleaned or replaced. You can get a technician to do this job for you. But you can save the labor charges by doing the replacement yourself. The choice is yours.

Replacing the flame rod by yourself isn’t a complicated task. Trust me, I’ve done it multiple times and I can tell that from my personal experience. If you want to clean or replace the flame rod assembly, follow these steps:

  1. Turn off the gas and power supply to the water heater. You can also turn off the water supply if you want but it’s not necessary.
  2. Depending on your model, you may have direct access to the flame rods. But you’d have to remove the blower to access the flame rods in some units.
  3. If you have to remove the blower, you’ll have to undo the three screws holding the blower in place. Then, you can twist it and pull it out. If you have direct access to the flame rods, you don’t have to remove the blower.
  4. Remove the screws holding the flame rod assembly in its place and disconnect the wiring from the connector.
  5. If you want to clean the flame rod, you can use an emery cloth or sandpaper to do it. However, if the gap between the flame rods has increased significantly, you should replace the entire assembly.
  6. Put the new flame rod assembly sits nicely in place of the old one and tighten the screws. Then, reconnect the wiring to the connector. Reverse engineer the above steps to put the heater back together.
flame rods of navien tankless water heater

That’s how easy it is to replace the flame rod assembly. No matter what you do, remember that the gas smell won’t completely go away forever. However, it’ll be managed a lot better by taking the right steps. If you notice a bad odor again coming for a long enough period, then you’ll have to take steps to fix it again.

03. Venting Issue

One of the possible causes behind your Navien water heater exhaust smelling like gas is a venting issue. The air and gas need to mix at the right ratio for proper combustion. Only then, there wouldn’t be unburnt gases left and you wouldn’t smell any air.

checking venting of navien tankless water heater

If there are any venting issues, that’s a recipe for disaster. If the air intake is frozen or clogged in any way, the unit won’t get sufficient air. So, the air-fuel ratio will be messed up and that can cause the exhaust to smell like gas.

Similarly, the exhaust termination also needs to be in line with the manufacturer’s recommendations. Any build-up of dirt or blockage in them can cause this issue.

How To Fix:

Check both the air intake and the exhaust vents properly. Make sure both of them are making a good connection to the collars in the heater. If any of them are loose, you need to tighten them.

Secondly, check the pipes for dirt and obstruction. Remove the debris from the pipes so that the required material can get into the heater. If the air intake pipes are frozen or too damaged, you need to replace them.

Make sure that both the intake and exhaust pipes are free of any blockage. Hopefully, doing that will bring down the gas smell from the exhaust. If the problem still remains, keep on reading to find the solution.

04. Loose Glass Gauge

You can’t have anything leaking as it’s a serious hazard. And that glass area is close to the heat exchanger. If it’s loose, the gas can leak from the heat exchanger and leave your tankless water heater smelling like gas.

glass gauge of navien tankless water heater

Check if the area around the heat exchanger seems loose to you by trying to wiggle it a little bit. You may also see the yellowish substance formed on them that we talked about earlier. Those are some clear signs of your tankless water heater having this issue.

How To Fix:

Tighten all the screws around the heat exchanger manually to make sure that there’s no gas leak. Steer clear of using any impacter or other powerful tools. If you do that, you’re risking breaking the heat exchanger.

If the heat exchanger gets damaged, it’ll cost you a fortune to replace the heat exchanger. So, use a Phillips head screwdriver and tighten each of the screws. If you do a good job there, no gas should be leaking. This solution is effective in both Natural Gas and Liquid Propane units.

05. Leaky Gas Line

While you may always suspect the tankless water heater to be leaking gas, it could also be the result of a bad gas line. If the gas line is clogged, it’ll interrupt the flow of gas. If it’s damaged, it’ll leak gas.

You can get a good idea if your gas line is leaking by smelling around it. While gas is naturally odorless, a chemical called “mercaptan” is added to it. The purpose of that is to identify gas leaks easily.

According to the words of Appollo Heating, “The chemical mercaptan is added to natural gas to better detect when a leak is occurring. This chemical has a distinct smell and is highly noticeable when a leak does exist”. So, smelling for a gas leak is the first test you should do.

The second thing you can do to check gas leak is to create a mixture of soapy water and spray it on the gas line. If there’s a leak anywhere, you’d see bubbles forming. That’s how you’d be able to tell that you have a bad gas line.

How To Fix:

If the tests reveal that you have a faulty gas line, you need to replace it. Do it as soon as you can as leaking gas is a dangerous problem. When you install a new gas line, I’d suggest you install a gas line that has protective polymer in it.

While the gas lines with protective polymer cost a little extra, they last longer and are less prone to leaks. So, investing in them is definitely worth it. Once you’ve got the replacement part, you can follow these steps to replace a faulty gas line in your home:

  1. Locate the gas pipe and inspect its connection to the water heater. Ideally, you should have enough room to work on the gas lines without any issues.
  2. Find the main gas line regulator or valve in your house and turn it off. Once it’s perpendicular to the gas lines, you’ll know that the gas line is off. Shut off the gas valve to the water heater as well.
  3. Remove the old gas line by popping it out of place. Set it aside and make sure you don’t smell too much of it for your own safety. Better yet, you should wear a mask when taking it off.
  4. Place the new gas line with protective polymer in place of the old one. Open the doors and windows in your house so that the remaining gas can escape.
  5. Turn on the main gas control valve and restore the gas supply to the water heater as well. You shouldn’t smell any gas after a while.

That’s how easy it is to replace the gas line on your own. If you still smell gas or the problem with your water heater remains, you should seek professional help. Remember that you won’t be able to solve all the problems on your own. Sometimes, you’d have to call in the experts.

Why Does My Navein Tankless Water Heater Smell Like Gas But There Is No Leak?

It’s a common scenario in Navein water heaters that you’d smell gas but there would be no gas leak. That’s because what you’re probably smelling is the residual gas mix. It was blown into the combustion chamber after ignition or before it took place.

There have been times when my customers have called about a gas leak issue. While they suspected the gas leak to come from their heaters, it came from another place. So, it’s also possible that what you’re thinking to be the culprit is actually functioning properly.

Sometimes, there could be a gas leak at the meter. But most people don’t notice the leak at the meter. Instead, they think it’s coming out of the exhaust termination. As a gas leak is no joke, these things should always be checked.

Hopefully, you’re not looking for a way around that in this guide. You need to have it checked as it could be a potential safety hazard. In most cases, you’d find no natural gas leaks but you’d find a high quantity of Carbon Monoxide when checking the products of combustion.

But when looking around the heater, there would be no CO. That’s what I found to be the case most of the time. And that’s a good thing because you don’t want any CO around the heater.

Luckily, you can do a quick smell test on your own to figure out the severity of the issue. Don’t put your face directly in the exhaust but you can be near the exhaust termination. Stay a foot or two away from the vents and then try to detect the odor.

If your unit is working properly, you won’t smell anything. But if there’s anything wrong, that’s more than enough distance to notice the odor. If you get a smell like rotten eggs, it’s indicative of natural gas.

But the smell can also be similar to that of car exhaust. That smell is actually an aldehyde odor. It’s usually the result of poor combustion. The right thing to do is to call a gas company to check this out. As it’s a serious matter, you should leave it to the experts to solve the problem.

How To Fix Gas Smell From Exhaust In Navien Tankless Heaters?

I’ve already talked about the major issues that could leave your water heater’s exhaust smelling like gas along with the fixes. But when it comes to gas, so much can go wrong. So, this section will be for additional tips to help you solve the issue.

For most of the solutions, you’ll require professional help. If you’re a DIYer, you won’t have all the tools required to test gas thoroughly. Firstly, check the main gas regulator if you have a natural gas water heater.

It’s possible that the gas is leaking from there but it makes its way to the exhaust as well. You can do a quick smell test first. If you have any reason to believe that there could be a leak, ask for the help of your gas company.

The gas regulator has to be tested at different loads to find out if it’s within the right specs. Using adequate tools, they’ll confirm whether there’s an issue and also take the appropriate steps to fix it. The second thing you should do is to ask Navien to send a technician with a combustion analyzer.

He’ll adjust the settings and that will minimize the problem as well. Even if the gas smell doesn’t completely go away, it should dwindle after changing the settings. It may be that way forever and that’s okay. It’s normal to get a little of the unburnt gas smell when you use a tankless water heater.

Another thing you can do to fix this issue is to run the exhaust vent pipes higher. Make sure you follow the manufacturer’s guidelines when setting up the exhaust termination. If you follow all these precautions, you’ll be able to keep this problem down to a minimum.

Can The Water In A Tankless Water Heater Smell?

The major difference between tankless and tank-style water heaters is that the water is heated on demand in tankless heaters. So, the water isn’t already preheated and stored in a tank as done in the tank-style water heaters.

When the water is heated in tank-style water heaters and stored, it promotes the growth of bacteria. That can lead to the rotten eggs smell that so many people complain about. But no water is stored in tankless units. So, it’s unlikely that the water from tankless units would smell.

However, it doesn’t mean that the water in tankless units smells. While it’s rare, the water in tankless heaters can produce pungent odors. The most likely reason behind this issue is a water leak.

So, if you’re facing this issue while using a tankless water heater, check the water system for leakage. The water leak could create an environment that promotes the growth of mold and mildew. So, if you find such a leak, you need to fix that immediately and nip this problem in the bud.

Why Does My Electrical Water Heater Smell Like Gas?

Electric heaters use a device called a heating element to heat the water. They don’t rely on gas as a fuel source. So, your electrical water heater wouldn’t smell like gas.

It’s possible that you’re mistaking a burning wire smell for a gas smell. There are many electrical connections in a water heater. If two wires make intermittent contact, that could create this issue.

So, you should consult an expert technician to solve this problem. Another common issue that you may face with your heater is that you have smelly water. That smell is due to the build-up of hydrogen sulfide in the water produced by the bacteria.

Using that water isn’t harmful but it’s understandable that it would be unpleasant for you. The main solutions here are to replace the anode rod at regular intervals and chlorinate the water to prevent bacteria buildup.

What Are Some Signs Or Symptoms Of A Gas Leak From A Water Heater Exhaust?

The most common sign of a gas leak is that you’d be able to smell it. They added the mercaptan chemical to the gas for a reason. But on top of that, there are a few more warning signs of a gas leak. Let’s go over them.

i) Dying Or Dead Plants

If you have any plants in your house, they could suffer due to a gas leak. Even if the plants are outside, they’ll be affected by the gas leak if it’s too severe. The soil will absorb the gas where it leaks and it’ll damage the plants in that area.

ii) Health Issues

Gas leaks can cause several health issues in humans. So, if the gas smell is accompanied by feelings of nausea or dizziness, that’s a serious issue. Feeling fatigued or tired is also a sign of carbon monoxide poisoning. So, there could be a big gas leak issue if you’re facing these health troubles.

iii) Hissing Sound

If you’re close enough to the source of the gas leak, you’ll hear a hissing sound. If you smell that sound around your heater, then there’s a strong chance of a leak. However, don’t go looking around for this sound as inhaling it would be dangerous. If you notice it, take corrective actions to fix the leak right away.

What Should You Do If There Is A Gas Leak?

Being caught up in a situation when there’s a gas leak is a tricky one. But if you keep a calm mind and take the right actions, you’ll be fine. Follow these steps if there’s a gas leak in your house:

Step 01: Shut Off The Gas Supply

Turn off the water heater and the main gas supply valve as well. You’d have to turn the gas valve completely perpendicular to the gas line to turn it off. Don’t try to overdo it as you may end up breaking the gas valve in that situation. Once you turn it off, the gas supply should be stopped.

Step 02: Open Doors And Windows

You don’t want the gas to keep building up in your home. So, open all the doors and windows so that the gas can escape to the outside environment. That’ll dissipate the gas from your house. So, you’ll have less exposure to the gas and there’ll be fewer chances of a major accident.

Step 03: Evacuate And Get Back When Safe

The final step is to evacuate your house and call for help. If you have children or pets, make sure you head out with all of them and wait for help to arrive. You can call a gas company or firefighters to solve this issue.

Don’t stay near your house unless it’s checked upon and is safe to enter. Once that issue is taken care of, you can reenter your home. Then, you can solve the heater problems that I’ve talked about to fix this issue permanently.

What Causes Tankless Water Heaters To Smell?

I’ve already addressed the gas-related issues that could lead to your tankless water heater smelling. But there are a few more common reasons why your heater can smell. Let’s take a quick look at them.

i) Burnt Wiring

You may think that your water heater is leaking gas but in reality, it’s possible that your hot water heater smells like burning wires. There are many electrical connections in a water heater. If any of them get shorted or start to burn, it’ll produce a smell.

The right thing to do in this situation is to turn off the water heater and unplug it to cause no further damage. Then, you can take off the front cover and inspect the wires. If any of them are burned, you need to replace them.

ii) Accumulation Of Dirt

As you keep using your water heater, dirt can build up inside it. With time, they can start to produce a smell. Thankfully, the fix here is simple. Remove the front cover of your heater and clean it with a dry cloth. Make sure to clean the area around the heater as well so that it doesn’t get filled with dust soon.

What To Do When There Is A Slight Gas Smell From Water Heater Valve?

If gas leaks occur in the right area, it can lead to an explosion. Especially, if it’s an area like a basement where there is low air supply. So, you shouldn’t underestimate even a slight smell if it comes from the valve.

Ideally, you should call a reputable company to check the issue and take care of it. If there’s a strong gas smell, you should do that right away. But if it’s not so severe yet, you can try to detect the leak.

Spray some soapy water or gas detection liquid on the connections you suspect could be leaking. If you see bubbles forming, it means you’ve found the weak point. From there on, you can take steps to seal the leak and fix the issue.

Why Heater Smells Like Gas When Off Only?

Normally, when you face a gas leak, it’ll be the most intense when the heater is on. Because that’s when the heater pulls in the gas and goes out through the leak. But another problem some people face is that the gas smell comes when the heater is off.

In this case, the most likely scenario is there would be a leak on the threaded gas pipe connection. The next common culprit behind this issue is a leaky gas shut-off valve. Either way, you should get help and follow the steps I’ve talked about whenever there’s a gas leak.

Can Carbon Monoxide Detectors Detect Gas Leak?

A lot of people think of installing CO detectors to become aware of a gas leak early on. But the truth is that they won’t detect all types of gas leaks. As the name suggests, CO detectors only detect the presence of Carbon Monoxide.

CO is really unburned gas. The build-up of Carbon Monoxide can be really dangerous to your health. Even if you burn kerosene or other fuel, CO is almost always realized as a byproduct.

Those types of CO can be odorless and impossible for humans to detect. Exposure to CO for a long time can cause dizziness and even death in extreme cases. So, I think that installing CO detectors is effective and there’s absolutely no harm in installing them.

But you can’t blindly rely on them for everything. When it comes to a regular gas leak, your nose will do a better job of detecting it than the CO detectors.


Should you route the exhaust vent pipes higher to dissipate the gas smells?

There are limits to how much you can extend the gas pipes. In most Navien units, you can extend the vent pipe to run a maximum of 100 feet and can have six elbows. Anything more than that is potentially dangerous.

Is it just Navien or do all tankless water heaters have this issue of the exhaust smelling like gas?

There are many tankless water heaters where the exhaust smells like gas. It’s a very common thing to happen during the ignition phase. Along with Navien, you’d also face this issue with Bosch and other tankless units.

Does a high amount of CO mean that your unit is not burning efficiently?

Yes, more CO indicates that the air-gas ratio is not ideal. It’s highly inefficient, will increase your gas bill, and is more dangerous by leaving CO deposits. Turning up the air or turning down the gas are two solutions to this issue.

Why do you see water vapor in the exhaust during cold weather?

When the water is cold, the temperature of the exhaust will be higher than the air in the environment. So, that automatically produces water vapor and that’s why you see them in the colder months.


Now you know the main reasons why your Navien tankless water exhaust smells like gas. The smell may not just come from the exhaust but from the heater or the main gas line as well.
Gas leaks can be very sensitive. So, make sure you follow the right safety precautions when dealing with this issue. Hopefully, it’ll be a simple fix and you’ll be able to use your heater soon. I have a guide on Navien water heater heat exchanger issues. Check it out if you’re interested.

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