I’ve worked on many Navien heaters over the last few years and solved countless issues. I became aware of the most common Navien tankless water heater error codes with time.
If you know what to do, it’s possible to solve many of these error codes by yourself. I’m creating this guide so that you’ll have a clear idea of how to deal with these error codes. So, let’s dive in!
Table of Contents
Navien Tankless Water Heater Error Codes [Complete Guide]
I’ll talk about the Navien error codes that pop up most frequently along with their solutions in this section.
01) E003 Error Code
The Navien tankless water heater error code E003 means that the unit has failed to ignite. There are several possible reasons behind this. But the most common ones are:
- The air intake filter is dirty.
- The heater isn’t getting power.
- The flame rod has gone bad.
- The heater doesn’t have a proper gas supply.
- The transformer has gone bad.
- The PCB is faulty.
How To Fix:
The right way to fix the E003 error code depends on what caused the issue in the first place. You’ll have to put on your detective glasses and diagnose the root cause of the issue.
I find a dirty air intake filter to be the culprit in the majority of the cases. A lot of dirt and debris can end up in there. So, the hater won’t get a proper air supply and it won’t ignite.
You need to remove the front cover of the heater to access the air intake filter. Once you see it, you can remove it by undoing a screw and pulling it off. When it’s free, clean it with a toothbrush and running water. Make sure you get all the dirt out of it and let it completely dry before you put it back in.
If the heater doesn’t have power, it could be due to a faulty power outlet or a glitch. You can reset the heater first to try to solve the issue. If that doesn’t work, turn the heater off and on. Check the power outlet with another device. If the outlet is faulty, you’ll have to replace it.
When the flame rods are bad, they won’t produce sparks and that would keep the heater from igniting. If the flame rod wiring is damaged, it won’t be able to communicate with the PCB and determine when to fire the sparks. So, you need to check them both. If any of them is damaged, replace it.
If the heater doesn’t have a proper gas supply, it means it either has no gas or the gas isn’t being supplied at the right pressure. If there’s no gas, it’s most likely because you have failed to pay your bills on time. Once you clear your dues, the gas supply issue will be solved and your heater will run normally.
You’d need a device called a manometer to check the gas pressure of the water heater. You should contact a qualified technician to inspect it for you. If any changes need to be made, then you should follow them to fix the issue and clear the E003 error code.
If either the transformer or the PCB is damaged, the faulty component will have to be replaced. You’ll be better off as the transformer is easier and cheaper to replace. However, if the PCB is truly faulty, you have no other option but to replace it if you want a permanent solution.
I’ve talked about the fixes in detail along with proper instructions for replacing the PCB in my Navien error code E003 how to fix guide. Check it out if you’re facing this error code so that you can find detailed guidelines on how to fix the issue and clear the code for good.
02) E016 Error Code
It’s a very common error code in Navien water heaters and it means that the heat exchanger is too heat. The most obvious reason behind the E016 error code is the calcification of your water heater. It usually happens due to a lack of maintenance of your water heater.
The water that goes through the heater isn’t fully pure and it leaves residue on the heat exchanger. When too much of it has piled up, the heat exchanger loses its efficiency. In that scenario, the heat exchanger can have a lot of scale and pop the error code.
How To Fix:
Thankfully, the problem isn’t too hard to fix. First, turn off the water heater for at least half an hour so that the heater has time to cool down. Then, you can restart the water heater. If the error code goes away, that’s good news as it means that the issue isn’t too severe.
However, you should be prepared that the error code can still come back when the heater is operational for a while. So, you’d have to flush the water heater to remove the scale build-up in the heat exchanger.
Once you get the dirt out of the heat exchanger, the error code will be properly fixed. I have a guide on flushing your Navien tankless water heater with step-by-step instructions on how you can flush the heater. You’ll need some tools to complete the flush.
So, make sure you gather everything you need and flush your water heater properly. However, keep in mind that flushing the heat exchanger isn’t a once-in-a-lifetime type of thing. You’d have to do it at least once or twice a year depending on the area where you live.
If your area has a more severe hard water supply, you’d have to do it more often. If the hardness of the water is low where you live, you can get by with a lot less flushing.
As a precaution, you can also install water softeners to reduce the hardness of the water before it goes to the heater. It’ll make sure that the heat exchanger gets filled with minimum impurities and can last longer.
In very rare cases, the heat exchanger may be damaged. In that case, flushing it won’t do the trick. You’d have to replace it to solve the issue. I have a dedicated guide on replacing a Navien heat exchanger if you want to learn more about it.
Keep in mind that it may make more sense to replace the heater altogether in some cases. Especially, if your unit has been used for a while and it’s no longer under any warranty.
03) E012 Error Code
The Navien tankless water heater error code 012 means that the flame is lost in the unit. It’s particularly annoying as you’ll most likely run out of hot water first before this error code even comes up.
So, you won’t be able to use any hot water until you fix this error code. A dirty air intake filter or the power supply not being properly grounded can cause this issue. So, make sure that you rule out these problems.
On top of that, there’s also the possibility that the flame rods are dirty or damaged. If they don’t work properly, they won’t be able to signal the flame and that can easily bring up the error code.
Apart from that, problems with gas supply may also be responsible here. If the gas isn’t being supplied at the right pressure, that can easily cause the Navien tankless water heater error code 12. The gas line could be undersized and that means less gas than required will enter the system.
There’s also the possibility that you have a bad gas regulator. It’s rare but still possible that the gas valve inside the tankless water heater is faulty. As there are many potential causes here, it’s very important to diagnose the error code properly before jumping to a conclusion.
How To Fix:
Depending on what’s causing the issue, the appropriate fix has to be implemented. It’s a good idea to start by cleaning the air intake filter. Then, check the power supply next.
The next thing you should look into is the flame rods. If they’re dirty, you can get by cleaning them. But if they’re damaged, you have to replace them. It may seem like a daunting task to change the flame rods but it’s not.
The important thing is to find the right part. If you want the part number to be an exact match, you may find it difficult to find the right replacement part. Even if the parts look the same, they may have different part numbers.
So, just be open to installing a new flame rod that doesn’t match the right part number as long as it looks identical. However, it’s always good to have the exact part number if you can get your hands on it. Otherwise, no biggie.
Replacing a flame rod is really easy. You’ll have to remove the front cover of the heater first and locate the flame rod. Here’s a picture to help you out so that you can easily find its location:
Next, you have to remove the black items as well as the wire. Make sure you don’t rip or tear the black boots when you remove them. After that, you’ll have to undo two screws at the left and right sides of the flame rod. When you remove it, you’ll be able to remove the flame rod from the water heater.
If the flame rod is dirty, you can just try to clean it first with sandpaper and reinstall it. However, if it still doesn’t work, it’s better to replace it. I recommend you replace it as it’s a more long-term solution.
If these things don’t solve the issue for you, contact a qualified technician. As they’ll have more expertise in determining an issue that’s related to the gas supply. Once the faulty component is diagnosed, it’ll have to be replaced. Doing so will clear the error code.
04) E011 Error Code
The error code E011 is an error code that can be easily triggered. It means ignition failure and you won’t have any hot water in this situation. The error code can most likely be triggered by the earthquake shutoff valve.
It’s quite easy to trigger the sensor. Even if you heat the tankless water heater while being on the move, the sensor can be triggered. A lack of gas supply can also lead to this issue.
A dirty gas manifold is often the most common culprit that leads to a lack of gas supply. So, the unit won’t get enough gas and the error code will come up.
How To Fix:
Proper diagnosis is once again the key to fixing the issue. If the earthquake shutoff valve is triggered, you can reset it and clear the error code. However, if the gas manifold is dirty, the unit will have to be cleaned.
It can be very difficult for a normal person without any technical expertise to clean the water heater. So, don’t hesitate to contact a qualified technician if you aren’t comfortable doing the job yourself.
However, proper maintenance of your water heater is a great way to prevent this issue from coming up in the first place. The key is to keep the internal heater clean from the inside as well as flush it from time to time.
05) E022 Error Code
The Navien tankless water heater error code 22 means that there’s an issue with the cold water outlet thermistor. Normally, it comes up when there’s an issue with the wiring of the thermistor or the thermistor itself.
How To Fix:
Check the wiring of the thermistor first. If it has come loose, you have to tighten it. If it’s damaged, you have to replace it. If the wiring is okay, the thermistor is most likely bad. In that case, you’ll have to replace it to clear the error code.
06) E004 Error Code
The Navien tankless E004 error code is another serious issue that means the unit has detected a false flame. It usually happens when the sensor that’s responsible for detecting the flame doesn’t pick it up.
A common reason behind it is that the power supply isn’t properly grounded. Apart from that, leaks in the heat exchanger can also cause it. A faulty circuit board can also trigger a false alarm and bring this error code.
A blockage in the venting system can also lead to an electrical short circuit in the PCB and bring up the E004 code.
How To Fix:
The main way to fix the problem depends on what’s bringing up the error code. If the power supply cable isn’t properly grounded, it can be easily fixed. However, other issues will be more challenging.
If the venting system is blocked or dirty, you can clean it out and that can solve the error code. But if it’s something more serious like a leaked heat exchanger, it’ll have to be replaced and that can get expensive. It’s also a code that you can easily prevent by maintaining your water heater properly.
07) E027 Error Code
The Navien tankless water heater error code 027 means that there’s excessive voltage passing through the system. It’s usually caused by a surge of power or malfunctioning electric components.
How To Fix:
As the power outlet is most likely at fault here, check it with a voltmeter. If it shows too much voltage, you need to replace it. Otherwise, it’s a good idea to consult an electrician to find out what’s causing the issue and fix it.
08) E110 Error Code
The Navien E110 error code comes up when there’s abnormal air pressure inside the water heater. There are many potential reasons behind it. The most common ones are:
- An exhaust pipe that’s blocked.
- A dirty air intake filter.
- The air intake vent is obstructed.
- Condensate has built up inside the unit.
How To Fix:
You’ll have to be on the lookout for all these issues and diagnose them as all of them can cause the error code. If the exhaust pipe or air intake vent is blocked, you need to inspect them to find it out. If any of them are clogged, remove the obstruction. Once the airway is clear, the error code should go away.
There’s also the possibility that the air intake filter is clogged. In that case, you’ll have to remove it from the water heater and clean it. It’s an easy process and there’s no reason you can’t do it on your own.
Finally, inspect the condensate drain of the water heater. If you see a build-up of condensate in them, you’ve found the culprit. Thankfully, it’s easy to fix by just draining the condensate.
I’ve gone through these solutions rather quickly because I have a dedicated guide on fixing the error code 110 on Navien tankless water heater. Check it out if you’re seeing this code and want to know about the solutions in detail. Hopefully, implementing the fixes will make the error code disappear.
09) E351 Error Code
The Navien tankless water heater error code 351 means an abnormal auto feeder valve. The water pressure detects a low level of water here and that leads to a low pressure in the heating pipe. So, the heater stops operating and automatically keeps refilling water.
However, when the auto feeder valve is functional for more than five minutes or so, the error code E351 comes up. So, the most common reason behind it is that the water pressure is low. Apart from that, the auto feeder valve itself can be faulty and trigger the code.
How To Fix:
There’s a simple solution to this problem if the issue is being caused by low water pressure. There’s a lever at the bottom of your water heater that you can push to increase the pressure in the system. However, I must advise you to proceed with caution.
When you pull the lever, you’ll hear the sound of water rushing through the heater. Don’t hold that lever for more than a few seconds at a time. If you hold it for a very long time in one go, your heater will be overpressurized and that can cause accidents.
You may have to do it a couple of times if you push the lever for a very short interval. But that’s completely fine. But keep in mind that the code may not disappear right away. So, you’d have to reset the heater to make it go away.
However, if the code still remains even after doing that, that means the auto feeder valve is most likely at fault. So, you’ll have to replace it with a new one to solve this issue.
If pushing the lever did the trick for you, that means something is causing low water pressure in your system. While it’s a temporary solution, the code may come back again when there’s low pressure.
So, it’s a good idea to consult a qualified technician to figure out what’s causing low water pressure and solve that problem for good. From my experience, it’s usually due to leaks in the water supply line. However, it may be something totally different for you.
10) E353 Error Code
Navien tankless water heater error code E353 means that the water pressure sensor isn’t working properly. The most common reason behind this is that the water pressure sensor is damaged.
How To Fix:
You’ll have to replace the water pressure sensor if you want to clear this error code. Don’t worry, it’s a really simple process to replace it. Just make sure that you order the right part number for your unit. You can follow these steps to replace the water pressure sensor in your Navien tankless heater:
Step 01 – Drain The Water
Drain the water from the tankless water heater. It’s really important because if you don’t do that, a lot of water will come out through the water pressure sensor when you remove it.
You can check out my guide on maintaining a Navien tankless water heater to learn about draining the water from the heater in detail over there. After draining the water, you’re ready to move on to the next step.
Step 02 – Remove The Old Water Pressure Sensor
You’ll have to remove the front panel of the water heater to access the water pressure sensor. You can easily do it by undoing the four screws that hold the cover in place. Two of them are located at the top and two will be at the bottom. Here’s what the pressure sensor looks like:
Then, remove the wiring connection that’s attached to the water pressure sensor. Have a sponge or piece of cloth ready before you remove the water pressure sensor.
Even if you’ve drained the water heater, a little water can still come out of the water pressure sensor. And of course, all the cold water and hot water lines should be closed at this stage. Then, unscrew the water pressure sensor and you’ll be able to pull it out.
Step 03 – Install The New Water Pressure Sensor
After removing the old sensor, you can put the new one in its place. Then, tighten it by screwing it in. Make sure that there are no leaks. Otherwise, water can come through it and damage the heater.
Then, turn on the water supply and double-check that there are no leaks. Once you’re satisfied that there are no leaks, you can attach the wiring of the pressure sensor. Put the front cover back in place and run the heater. Hopefully, the error code will go away at this stage.
11) E445 Error Code
The Navien tankless E445 error code indicates an issue with the mixing valve in the water heater. Another common name for it is the water adjustment valve. When it gets damaged, the error code pops up.
How To Fix:
Thankfully, the solution here is simple as the mixing valve is really easy to replace. Once you remove the front panel of the water heater, you’ll see two water adjustment valves. You may be confused as to which one is damaged. It’s the one on the right. Here’s a picture to help you out:
Make sure you turn off the water heater and close all the hot and cold water valves. Relieve the pressure inside the water heater as well before you start replacing the valve.
There are a couple of retaining clips that hold the mixing valve in place. Once you remove both of them, you’ll be able to pull it out. Then, replace it with a new one and put the retaining clips back on. It’ll seal the mixing valve in its place and make sure that it doesn’t move.
Once you’re happy with the replacement, turn the hot and cold water valves back on. Restore the power to the water heater. Check that there are no leaks and if there are, you need to tighten the installation you just made. Hopefully, the error code will go away after replacing the faulty valve.
12) E515 Error Code
This error code indicates abnormal PCB operation. The most interesting thing about this code is that it’s usually followed by a subcode that reveals the reason why the code came up.
The subcodes are usually 9,10,11 or 12. The Navien tankless water heater error code 515-09 indicates abnormal communication between the PCB and the fan. So, the fan can be damaged here and cause this code. It’s also possible that the wiring between the fan and the PCB is compromised.
The Navien 515-10 error code means an abnormal monitoring device of the PCB. The fault could be with the dual venturi or the PCB connection. If you see subcode 11 or 12, remember that it also happens for the same reason as subcode 10. So, you’ll have to go through the same diagnostic process.
How To Fix:
First, ensure that the electrical power is grounded and there are no issues with the power supply. If there are any electrical interferences of the PCB, it can also lead to its abnormal operation. So, rule out this issue before you do anything else.
The subcode will give you a good idea of what you should do to clear the error code. The error code 515-09 Navien tankless water heater can be solved by replacing the fan if it’s faulty. If the wiring or PCB is damaged, they’ll also have to be replaced to clear the error code.
Similarly, the dual venturi could be damaged and they may also have to be replaced for error subcodes 10-12. The worst-case scenario when you’re facing this error code is a damaged PCB. That’s because it can be expensive to replace, especially, if you need a qualified technician for this job.
13) E438 Error Code
The Navien error code E438 represents the abnormal operation of the circulation pump. There are both external and internal problems that could lead to this issue and cause this error code. The most common reasons behind this code are:
- A blocked cold water inlet filter.
- Not fully opening the water lines.
- The flow sensor is damaged.
- The circulation pump is faulty.
- The 2-way valve is facing the wrong direction.
How To Fix:
If the cold water inlet filter is dirty, you’ll have to clean it. Thankfully, it’s a very easy job as all you’ll have to do it to locate it and pull it out. Then, clean it under running water and reinstall it. Check if that fixes the error code.
To make sure the water lines are okay, you’d have to check the main water supply line in your home as well as the water heater. Double-check that the main water line is fully perpendicular to the pipes and you can’t turn them any further. Similarly, ensure that all the valves in the water heater are open.
The next possibility is that the flow sensor is damaged. If it’s faulty, it’ll have to be replaced. The same goes for the circulation pump. If it’s no longer functioning, you have no other choice but to replace it to clear the error code.
If the 2-way valve isn’t facing the right direction, you can adjust it to make the error code go away. But there’s also a chance that it can be damaged. In that case, you’ll have to replace it.
I have a guide on fixing Navien E438 code where I talk about these problems and solutions in detail. You’ll also find detailed instructions on replacing the flow sensor, circulation pump, and 2-way valve over there. I highly recommend you check out that guide if you’re facing this error code.
14) E030 Error Code
This error code means that the exhaust of the Navien tankless water heater has overheated. Depending on the type and model of the heater, it can get triggered at different temperatures.
For some models, you’ll see this error code come up when the flue temperature goes higher than 149°F or 65°C. However, there are other models in which the code will get triggered when the temperature of the flue exceeds 230°F or 110°C for more than 10 seconds.
The most common reason behind it is if the heater has been running for too long. Then, there’s the possibility that the cold water inlet filter is dirty. On top of that, a heat exchanger with a high amount of scale build-up can also make this error code pop up.
How To Fix:
The first thing you should try is to shut off the heater for a while. Make sure that it remains off for at least half an hour. Once that period has passed, you restart the heater and see if the code goes away.
If the error code remains, it’s a good idea to turn it off again and clean the cold water inlet filter. While you’re at it, make sure that the dipswitch settings and the water adjustment valve are okay.
Then, restore the power supply to the water heater. If you still see the code come up, then it’s essential to flush the heat exchanger. Once you do that, the error code should disappear.
15) E031 Error Code
When you see this error code, it means that the PCB is getting a signal that the burner is overheating. It’s a common error code in Navien boilers. It usually comes up when the high-limit switch has failed.
How To Fix:
You’ll have to replace the high-limit switch in your Navien tankless water heater with a new one. It’s a relatively inexpensive component and also very easy to replace.
I’m sure that you can do it on your own after watching a couple of tutorials. However, if the error code remains even after replacing it, the problem could be more complex. So, you’ll have to consult a qualified technician to diagnose the issue for you and solve it.
16) E047 Error Code
The Navien tankless water heater error code E047 indicates abnormal operation of the exhaust thermistor. It’s a device that’s responsible for monitoring and regulating the temperature of the exhaust gases.
Firstly, there’s a possibility that the exhaust thermistor is open. In that case, it may be no longer connected or gone bad. Secondly, it can also be shorted and that usually happens when it doesn’t have a good connection with the PCB of the heater.
How To Fix:
Start by checking the wiring of the exhaust thermistor. If it’s damaged, you can replace it to make the error code go away. Then, check its connection to the PCB. If it’s disconnected or loose, you can reconnect it and make sure that it stays nice and tight.
However, if both these things are okay, then there’s the possibility that the thermistor is bad. In that case, you’ll have to replace it. You can either do it yourself or hire an expert for this job.
17) E060 Error Code
Encountering the Navien E060 error code means that the dual venturi in your heater isn’t working normally. The dual venturi is important as it optimizes the flow of gas and air into the water heater.
Abnormal operation of the dual venturi usually happens due to a fault of the dual venturi limit switch. The switch can be either stuck in an on or off position or function abnormally.
Apart from that, the abnormal operation can also be the result of obstructions in the gas orifice. If you’re facing this error code, you should work quickly to find a way to fix it.
How To Fix:
Begin fixing the error code by checking the connection of the dual venturi first. If it’s loose or damaged, fix it and that’ll take care of the problem. Secondly, test whether the dual venturi is working properly.
You can do it by using the TEST mode in your water heater. If there are issues with the functionality of the dual venturi, you’ll have to replace it with a new one. If the gas orifice is dirty, it needs to be cleaned.
After doing all these things, the error code is supposed to go away. If it still remains, you have no other option but to consult an expert to diagnose and fix this error code.
18) E109 Error Code
When you see the E109 error code pop up on your Navien tankless water heater, it means that the fan in the unit isn’t working properly. There are many potential reasons behind it.
The most common one is a dirty air intake filter. If the filter is dirty, enough air won’t be able to go to the fan. So, it won’t function normally and that’s why the error code comes up.
Besides that, power issues can also lead to the fan not operating properly. There’s also the possibility that the fan motor itself is dirty or damaged. All of these things will make this error code come up.
How To Fix:
You should clean the air intake filter before doing anything else. It’s very easy to do and only takes a few minutes. I’ve already shown you how you can do that. However, if the air intake filter is clean or the code still remains after you clean it, it’s caused by another issue.
Next, you should inspect that the fan has a proper power supply by checking the power supply and the voltage. Inspect the wiring and make sure that it’s not damaged.
Check the condition of the fan motor as well. If it’s dirty, cleaning it will clear the error code. But if it has gone bad, you’ll have to replace the fan with a new one to remove the error code.
19) E407, E421, E432 & E441 Error Code
I’ve put all these error codes into the same category because they’re all related to the thermistor. The only difference depending on the error code is which thermistor is at fault. Here’s a list of the thermistors that are responsible for the error code:
- E407 – The hot water outlet thermistor is operating abnormally.
- E421 – The cold water inlet thermistor is operating abnormally.
- E432 – The second cold water inlet thermistor is not functioning properly.
- E441 – The second hot water inlet thermistor is not functioning properly.
How To Fix:
The way to fix the error code is pretty much the same for all these error codes. You’d have to check the thermistor in question and replace it if it turns out to be faulty. When you do that, the error code should go away.
20) E434 Error Code
This code indicates abnormal operation of the water adjustment valve. The most likely scenario here is that the valve is either stuck in an open or closed position. Apart from that, the water adjustment valve being loosely connected to the heater can also trigger the code.
How To Fix:
Inspect the connection of the valve to the heater. If it’s loose, you can tighten it. If it is tight, then the water adjustment valve is faulty. You’ll have to replace it with a new one to make the error code disappear.
21) E439 Error Code
If you see the E439 error code in your Navien tankless water heater, it means the flow sensor isn’t working properly. It comes up when the cold water inlet filter is clogged or the flow sensor itself is faulty.
How To Fix:
Begin the fixing process by inspecting the cold water inlet filter first. It’s much easier to check and clean it if it’s dirty. You should already be familiar with how to do it as I’ve talked about it earlier.
If the error code remains after you’ve cleaned it or it was already clean, you have to inspect the flow sensor. It’ll most likely be defective and you’d have to replace it with a new one to clear the error code.
22) E517 Error Code
This Navien 517 error code indicates the abnormal operation of the DIP switch. It usually happens when the DIP switch settings are messed up. You’ll be able to access the DIP switch settings from both the control panel as well as the PCB of the heater.
The DIP switch settings must be set up correctly. If they’re not in the right order, this error code will come up and your heater won’t function properly.
How To Fix:
You have to check the DIP switches at both the PCB and the front panel of the water heater. Make sure that they are in accordance with the recommended settings by Navien. Once you correct the settings, the error code will most likely go away. If it still remains, consult a qualified technician.
23) E594 & E615 Error Code
The reason why the Navien tankless E594 error code comes up depends largely on the subcode that’s next to it. If the subcode is 0, it indicates that the data received from the high-limit switch is abnormal. Similarly, here’s a list of the meaning behind all the other subcodes:
- 1 – The input data from the exhaust sensor is abnormal.
- 2 – The input data from the flame rod is not normal.
- 3-14 – The memory of the PCB is abnormal.
- 15 – The input data from the pressure sensor is below the accepted range.
- 16 – The input data from the pressure sensor is above the accepted range.
Now, the same problems are represented with the error code 615 in some heaters depending on the model. They both mean the same thing even down to the subcodes. So, E615-1 means that the exhaust sensor input data is abnormal and so on.
How To Fix:
For the 594-0 error code, check the PCB and make sure the connections are tight. For 594-1, check the exhaust sensor wiring and the sensor itself. If any of them are faulty, you need to replace them.
For 594-2, inspect the flame rod and the flame rod wiring. If they’re damaged, you have to replace them. I already showed you how you can do that in an earlier section. It’s a really easy process.
For subcodes 3 to 14, check the PCB and make sure that everything is in order. Finally, for subcodes 15 and 16, check the wiring and the output voltage of the pressure sensor. If the wiring is okay, that means the sensor itself is bad and you need to replace it.
24) E598 Error Code
The Navien tankless water heater error code 598-00 is common in the 180A2 and 180S2 units. The most common reason why it comes up is due to abnormal RTC. RTC stands for Real Time Clock. So, this code comes up when the date and time settings of the water heater are incorrect.
It may happen due to a power outage and the heater losing the previous settings when it’s turned back on. But if the date and time settings are okay, that means you’re in a big problem. That’s because the code is most likely being caused by a faulty PCB in this case.
How To Fix:
Thankfully, solving abnormal RTC issues is easy. You just have to go to the time and date settings in your heater and adjust them. You can access it by going to the settings menu in the keypad of your water heater.
After you complete this procedure, the error code may not disappear right away. You should reset the heater to make sure that the error code goes away for good.
The good news is that Navien tankless water heaters are extremely straightforward to reset. All you have to do is press the reset button on the keypad and that’ll do the trick. If it keeps coming back, that means you have a faulty PCB and you’ll need to replace it to clear the code.
25) E736 Error Code
The Navien tankless water heater error code 736 means that the cascade operation is not normal. It usually comes up when the ready-link cable is damaged. Besides that, the cascade settings not being correct or the PCB not being compatible can bring up this code.
How To Fix:
Start by checking the ready-link cable. If it’s faulty, you have to replace it to take care of the issue. Otherwise, either the cascade settings will have to be reconfigured or the PCB version will have to be altered.
If you don’t have prior experience working with Navien water heaters, you may be confused in terms of what to do. So, contact the Navien tech support team to help you out with your problem.
26) E740 Error Code
There’s an outdoor temperature sensor in the Navien water heater. The error code 740 appears when the sensor acts abnormally. It only happens when the outdoor reset curve is enabled. The reason behind this code is either the sensor is stuck open or has an electric short.
How To Fix:
You have to check the outdoor sensor curve and make sure that it’s set properly to clear the error code. Double-check that the wiring connection is not damaged. If it’s not in good condition, replace it and hopefully, doing that will make the error code disappear.
27) E760 Error Code
Technically, this isn’t an error code. It’s a flushing alarm. Basically, the system is reminding you that it’s high time you flush the water heater. There’s probably a lot of scale build-up at this point and that’s why the system is recommending that you flush the heater.
How To Fix:
It’s quite obvious – you have to flush the heater to clear the error code. If you’ve never done it before, then there’s no need to worry. I’ve done it hundreds of times and let me tell you that anyone can do it.
Keep in mind that you do need a good flushing kit to flush the water heater properly. The most items are a pump and a cleaning solution. The pump will run the cleaning solution through the heater. You can also use white vinegar as a clearing solution.
I have a detailed guide on flushing a Navien tankless water heater where I walk you through this entire process in detail. Follow the steps I showed there. If you do, I don’t think you’ll have any problems in flushing your water heater.
28) E762 Error Code
The Navien error code 762 means there’s most likely an issue with the exhaust vent. The main reason behind getting this code in Navien heaters is not installing the vent correctly. Let’s learn about why this error code was introduced in the first place.
Initially, a common mistake made by many trained individuals when installing Navien water heaters is using street 90s on top of the exhaust outlet to start the vent run. The issue with them is that they don’t cover the vent connection enough to prevent carbon monoxide from getting in there.
So, this was a maj