Navien tankless water heaters and combi-boilers show a code such as E003 or E012 on the front panel display. Below are 28 Navien codes across 1 model series. Each one says what it means, which series it applies to, what you can safely check, and when to call a licensed pro, with a link to the Navien document it comes from.
The same code can mean different things on different series, so match the series column to your unit. Your unit's manual is the final word. Reviewed October 2026.
28 codes
| Code | Meaning | Applies to | Safety |
|---|---|---|---|
| E003 Error code shown on the front panel display | Ignition failure | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E004 Error code shown on the front panel display | False flame detection | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E012 Error code shown on the front panel display | Flame loss | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E016 Error code shown on the front panel display | Overheating of heat exchanger | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E030 Error code shown on the front panel display | Exhaust overheating | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E031 Error code shown on the front panel display | Overheating of burner | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E046 Error code shown on the front panel display | Limit control abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E047 Error code shown on the front panel display | Exhaust thermostat thermistor open or short circuit | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E060 Error code shown on the front panel display | Dual venturi abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E109 Error code shown on the front panel display | Fan motor abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E110 Error code shown on the front panel display | Abnormal air pressure | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E407 Error code shown on the front panel display | Hot water outlet thermistor open or short circuit | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E421 Error code shown on the front panel display | Cold water inlet 1 thermistor open or short circuit | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E432 Error code shown on the front panel display | Cold water inlet 2 thermistor open or short circuit | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E434 Error code shown on the front panel display | Water adjustment valve abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E438 Error code shown on the front panel display | Circulation pump abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🧭 Check first |
| E439 Error code shown on the front panel display | Flow sensor abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E441 Error code shown on the front panel display | Hot water inlet 2 thermistor open or short circuit | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E445 Error code shown on the front panel display | Bypass mixing valve abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E515 Error code shown on the front panel display | PCB abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E517 Error code shown on the front panel display | DIP switch setting abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E593 Error code shown on the front panel display | Front panel key abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E594 Error code shown on the front panel display | EEPROM abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E615 Error code shown on the front panel display | Input and memory abnormal operation | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E760 Error code shown on the front panel display | Flushing/service alarm | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | ✅ Keep running |
| E762 Error code shown on the front panel display | Vent pipe not properly inserted | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E773 Error code shown on the front panel display | Wrong gas | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
| E788 Error code shown on the front panel display | Gas type setting mismatch | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters | 🛑 Call a pro |
✅ Usually fine to keep running · 🧭 Check a few things first · 🛑 Turn it off and call a licensed pro
The codes Navien documents for each series we have checked. If your series is not listed, the code may mean something different on your unit, so check its manual.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists this as overheating of the burner and tells you to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists an abnormal operation of the limit control and tells you to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists an abnormal operation of the dual venturi and says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The cold water inlet 2 temperature sensor circuit is open or shorted. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The flow sensor is not operating normally. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
This sensor circuit is open or shorted. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The bypass mixing valve is not operating normally. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The DIP switch setting is abnormal. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
A front panel key is not operating normally. The manual says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists an abnormal operation of the EEPROM memory and says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists an abnormal operation of input and memory and says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The manual lists that the vent pipe is not properly inserted and says to contact customer support.
When to call a pro: Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
Applies to: NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters. Shows as: Error code shown on the front panel display
The gas type set on the panel DIP switch does not match the gas type setting on the panel. The manual says to check the supplied gas type and make them match.
When to call a pro: Have a licensed technician or the installer confirm the gas type and correct the settings.
Ryan Giles · Red Seal Certified Plumber · Ask a plumber · Ask an HVAC technician