Navien Tankless Error Codes: Owner's List
On this page (7 sections)
The Short Answer: Navien shows faults as an E followed by three digits. In the NPE-2 and NPN owner manuals, only a handful have an owner check: E003 (open the gas valve), E012 and E109 (clean the intake filter), E016 and E030 (clean the inlet water filter, flush), E110 (clear the vent), grounding for E004 and E515, and installer service for E760 and E788. Most others say to contact technical support.
Find your model first
The tables differ between product lines. Check the model number on the rating label on the side of the cabinet:
- NPE-A2 or NPE-S2 (for example NPE-240A2): condensing, current generation. Use the main table below.
- NPE-A or NPE-S without the 2: older condensing models. Mostly the same table; differences are noted below it.
- NPN (for example NPN-199U): non-condensing. See the NPN section.
- NCB combi-boilers use their own table, which includes heating codes such as E205 and E351.
NPE-A2 and NPE-S2 codes with an owner check
These come from the troubleshooting table in the NPE-2 user’s information manual (opens in a new tab). Do the listed check, then reset by pressing the Back button.
| Code | Meaning in the manual | What Navien lists |
|---|---|---|
| E003 | Ignition failure | Make sure the main gas supply valve is open. See Navien E003 |
| E004 | False flame detection | Make sure the electrical cord is properly grounded |
| E012 | Flame loss | Clean the intake air filter; make sure the cord is properly grounded |
| E016 | Overheating of heat exchanger | Clean the cold water inlet filter; flush the heat exchanger |
| E030 | Exhaust overheating (shuts down when flue temperature exceeds 149°F) | Clean the cold water inlet filter; flush the heat exchanger |
| E109 | Abnormal operation: fan motor | Clean the intake air filter |
| E110 | Abnormal air pressure | Make sure the exhaust pipe is free of obstructions; clean the intake air filter. See Navien exhaust or air intake blocked |
| E438 | Abnormal operation: circulation pump (with an air handler installed) | Check that the circulation pump is operating |
| E515 | Abnormal operation: PCB | Make sure the electrical cord is properly grounded |
| E760 | Flushing or service alarm | Contact the installer for routine service |
| E788 | Gas type on the panel DIP switch doesn’t match the panel setting | Check the supplied gas type and match the settings (installer work) |
The inlet water filter and intake air filter are owner maintenance items in the manual. For E016 and E030, the manual also lists flushing the heat exchanger. If the heater has never been descaled, or you don’t have the isolation valves and pump to do it, ask the installer. E016 and E030 often show up as hot water that turns cold; see Navien goes cold after a few minutes.
NPE-A2 and NPE-S2 codes that need technical support
For these the manual’s only action is to contact Navien technical support (1-800-519-8794) or an authorized technician:
| Code | Meaning in the manual |
|---|---|
| E031 | Overheating of burner |
| E046 | Abnormal operation: limit control |
| E047 | Exhaust thermostat: thermistor open or short circuit |
| E060 | Abnormal operation: dual venturi |
| E407 | Hot water outlet thermistor open or short circuit |
| E421, E432 | Cold water inlet thermistor 1 or 2 open or short circuit |
| E434 | Abnormal operation: water adjustment valve |
| E439 | Abnormal operation: flow sensor |
| E441 | Hot water inlet 2 thermistor open or short circuit |
| E445 | Abnormal operation: bypass mixing valve |
| E517 | Abnormal operation: DIP switch setting |
| E593 | Abnormal operation: front panel key |
| E594 | Abnormal operation: EEPROM |
| E615 | Abnormal operation: input and memory |
| E736 | Abnormal operation: cascade communication |
| E740 | Outdoor temperature sensor (with an air handler installed) |
| E762 | Vent pipe not properly inserted |
| E773 | Using the wrong gas. See Navien E773 |
| E782 | Abnormal operation: main panel communication |
| E785 | Flow switch or sensor (with an air handler installed) |
Navien’s January 2026 installation manual (opens in a new tab) adds that E773 can appear even when the gas type and setting are correct, because of measuring tolerances in the unit. If it persists with matching settings, Navien asks you to contact technical support.
Older NPE-A and NPE-S
The older NPE user’s manual (opens in a new tab) uses nearly the same table, with a few differences:
- For E016 and E030, the first step is to turn the system off for at least 30 minutes, then restart it, before cleaning the filter or flushing.
- E438 refers to the recirculation plumbing: with external recirculation, make sure all supply and return lines are open; with internal recirculation, check the direction of the 2-way valve.
- E031, E594, E762, E773 and E788 aren’t listed.
- These models reset with a dedicated Reset button rather than the Back button.
NPN non-condensing codes
The NPN user’s manual (opens in a new tab) shares many codes but differs in a few important ways:
| Code | Meaning in the NPN manual | What Navien lists |
|---|---|---|
| E003 | Ignition failure | Main gas valve open; gas manifold and fuel DIP switch must match the supplied gas (installer check) |
| E004 | False flame detection | Cord properly grounded |
| E012 | Flame loss | Clean the intake air filter; grounding; manifold and DIP switch must match the gas |
| E016 | Overheating of heat exchanger | Turn off for at least 30 minutes and restart; clean the inlet filter; flush |
| E109 | Fan motor | Contact technical support (unlike the NPE, there’s no owner check) |
| E110 | Abnormal air pressure | Make sure the vent pipe is free of obstructions |
| E438 | Circulation pump | External recirculation: make sure supply and return lines are open |
| E515 | PCB | Cord properly grounded |
| E760 | Flushing or service alarm | Contact the installer for routine service |
The NPN table also lists E056 (modulating gas valve), E127 and E157 (air volume), E170 (antifreeze heater), and E786 (panel connection). On NPN models E773 is described as “abnormal operation: gas connection.” All of these go to technical support. The NPN has no E030, E031, E047, E060, E432 or E788.
About codes like 598-00 and 773-00
The manuals above all show three-digit codes after an E. Some owners report codes written with a two-digit suffix, such as 598-00. Navien’s owner documentation doesn’t explain that format, and 598 isn’t in any of these tables. Read the three digits before the dash against the table for your model, and confirm anything not listed with Navien. What is known about one of them is in Navien error 598-00.
To clear a code after fixing its cause, see how to reset a Navien tankless water heater.
Frequently Asked Questions
Q: The same code keeps coming back after I reset it. What should I do? A: Do the owner check for that code once. If it still returns, stop resetting and call your installer or Navien with the model, serial number and the error history from the front panel.
Q: Do E016 and E030 mean my heat exchanger is ruined? A: Not by themselves. Both are overheating codes, and Navien’s first remedies are a clean inlet filter and a flush. Scale from hard water restricts flow through the heat exchanger, which is why flushing is on the list. If the code returns after a flush and a clean filter, a technician needs to look further.
Q: Why does my code list differ from the one in my manual? A: Navien revises its tables between product generations and manual editions. The tables here come from the editions linked above; if your manual differs, follow the one for your exact model.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Navien: User's Information Manual, NPE condensing water heaters (NPE-A2/S2), part 20049624A (opens in a new tab)NPE-180A2/210A2/240A2 and NPE-180S2/210S2/240S2; troubleshooting table.
- Navien: User's Information Manual, NPE condensing water heaters (older NPE-A/S, Version 5.3) (opens in a new tab)NPE-180A/210A/240A and NPE-150S/180S/210S/240S; troubleshooting table.
- Navien: User's Information Manual, NPN non-condensing water heaters, part 20045995B (opens in a new tab)NPN-160U/180U/199U and NPN-120E/160E/180E/199E; troubleshooting table.
- Navien: Installation Manual, NPE condensing water heaters (Version 2.0, January 2026) (opens in a new tab)NPE-A2/S2; E773 explanation and level 1 errors.
- Navien: User's Information Manual, NCB-H combi-boilers (Version 1.0, April 2024) (opens in a new tab)NCB-H combi-boilers; heating error codes such as E205 and E351.
- Navien: manuals and product documents (opens in a new tab)Model-specific owner information; service manuals are intended for qualified professionals.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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