Navien tankless water heater error codes
37 codes for NPE-A2, NPE-S2, NPN, each with the wording and page from Navien's manuals.
All Navien codes
Meanings are quoted from Navien's manuals. The "Who" column is our reading of the manual's remedy: whether an owner can do the first checks, or the fix belongs to a licensed technician.
| Code | Manual meaning | Series | Who | Source |
|---|---|---|---|---|
| E003 | “Ignition failure” What to check | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E004 | “False flame detection” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E012 | “Flame loss” What to check | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E016 | “Overheating of heat exchanger” What to check | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E030 | “Exhaust overheating (the water heater shuts down when the flue temperature exceeds 149 °F (65 °C)” What to check Quoted as printed: the closing parenthesis is missing in the manual. | NPE-A2, NPE-S2 | Owner checks, then technician | NPE-2 user's manual p. 17 |
| E031 | “Overheating of burner” | NPE-A2, NPE-S2 | Technician | NPE-2 user's manual p. 17 |
| E046 | “Abnormal operation: limit control” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E047 | “Exhaust thermostat: thermistor open or short circuit” The NR-21DU Remote Controller Manual lists this code as “Abnormal operation: exhaust thermostat” (p. 30). | NPE-A2, NPE-S2 | Technician | NPE-2 user's manual p. 17 |
| E056 | “Abnormal operation: Modulating gas valve” | NPN | Technician | NPN user's manual p. 22 |
| E060 | “Abnormal operation: dual venturi” | NPE-A2, NPE-S2 | Technician | NPE-2 user's manual p. 17 |
| E109 | “Abnormal operation: fan motor” What to check | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E110 | “Abnormal air pressure” What to check | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E127 | “Abnormal operation : Air volume Open/Short/Default value/No answer” | NPN | Technician | NPN user's manual p. 22 |
| E157 | “Abnormal operation : Air volume control” | NPN | Technician | NPN user's manual p. 22 |
| E170 | “Antifreeze heater Open/Short” | NPN | Technician | NPN user's manual p. 22 |
| E407 | “Hot water outlet: thermistor open or short circuit” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E421 | “Cold water inlet1: thermistor open or short circuit” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E432 | “Cold water inlet2: thermistor open or short circuit” | NPE-A2, NPE-S2 | Technician | NPE-2 user's manual p. 17 |
| E434 | “Abnormal operation: water adjustment valve” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E438 | “Abnormal operation: circulation pump (in case of installed AHU)” The NPN User's Information Manual (p. 22) and the NR-21DU Remote Controller Manual (p. 31) list it as “Abnormal operation: circulation pump”, without the AHU condition. Both give the remedy “External: Ensure that all water supply and return lines are open.” | NPE-A2, NPE-S2, NPN | Owner checks, then technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E439 | “Abnormal operation: flow sensor” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E441 | “Hot water inlet2: thermistor open or short circuit” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E445 | “Abnormal operation: Bypass mixing valve” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E515 | “Abnormal operation: PCB” The NR-21DU Remote Controller Manual lists this code as “Abnormal operation: controller” (p. 32). | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 22 |
| E517 | “Abnormal operation: DIP switch setting” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 23 |
| E593 | “Abnormal operation: front panel key” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 23 |
| E594 | “Abnormal operation: EEPROM” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 23 |
| E615 | “Abnormal operation: input and memory” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 17; NPN user's manual p. 23 |
| E736 | “Abnormal operation: cascade communication” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E740 | “Abnormal operation: outdoor temperature sensor (in case of installed AHU)” The NPN User's Information Manual lists it as “Abnormal operation: outdoor temperature sensor”, without the AHU condition (p. 23). | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E760 | “Flushing/service alarm” What to check | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E762 | “Vent pipe not properly inserted” What to check | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E773 | “Using the wrong gas” The NPN User's Information Manual lists it as “Abnormal operation: gas connection” (p. 23). Both installation manuals call E773 an “Improper Gas Type Detection Warning” and say it can appear even with the correct gas type and setting (NPE-2 Installation & Operation Manual, p. 19; NPN Installation and Operation Manual, p. 19). | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E782 | “Abnormal operation: main panel communication” | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E785 | “Abnormal operation: flow switch/sensor (in case of installed AHU)” The NPN User's Information Manual lists it as “Abnormal operation: flow switch/sensor”, without the AHU condition (p. 23). | NPE-A2, NPE-S2, NPN | Technician | NPE-2 user's manual p. 18; NPN user's manual p. 23 |
| E786 | “Abnormal operation: panel connection” | NPN | Technician | NPN user's manual p. 23 |
| E788 | “Abnormal operation: Discrepancy with the gas type on the panel DIP S/W setting and the panel” | NPE-A2, NPE-S2 | Technician | NPE-2 user's manual p. 18 |
How to read a Navien code
The code appears on the heater’s front panel display NPE-2 User’s Information Manual, p. 17. The NR-21DU remote shows it as three digits next to a flashing red LED and an error icon. Depending on the fault, the heater either stops or keeps only basic operation NR-21DU Remote Controller Manual, p. 26.
Navien’s tables write codes as E plus three digits, such as E003. On NPE-A2 and NPE-S2 models, Menu, then 3. Error History, lists the 10 most recent errors, and the manual’s example shows an entry as “Err 003 - 00” NPE-2 Installation & Operation Manual, p. 96. The manuals do not explain the digits after the dash.
Use the table for your model number:
- NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2: NPE-2 User’s Information Manual, Version 1.0 (2020), pp. 17–18.
- NPN-160U, NPN-180U, NPN-199U, NPN-120E, NPN-160E, NPN-180E, NPN-199E: NPN User’s Information Manual, Version 1.0 (December 2020), pp. 22–23.
The NPE-150S2 is not on the cover of the NPE-2 user’s manual, so Navien’s documents do not confirm that its code table covers that model.
Clearing a code
On NPE-A2 and NPE-S2 models, press Back NPE-2 User’s Information Manual, p. 10. On NPN models, press Reset on the front panel. Outdoor NPN models reset with one press of OK on the remote, and “RST” appears NPN User’s Information Manual, pp. 12, 21.
The NPE-2 installation manual describes “level 1” errors, which let the heater keep running and clear once the problem is fixed. It does not say which codes are level 1 p. 96.
If the code comes back after a reset, do the remedy listed for that code. If the code still returns, contact an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 NPE-2 User’s Information Manual, p. 16; NPN User’s Information Manual, p. 21.
When to stop and call a professional
If you smell gas, do not touch electrical switches or try to light any appliance, and call your gas supplier from a neighbor’s phone and follow their instructions, or the fire department if you cannot reach the supplier NPE-2 User’s Information Manual, p. 1.
Navien tells owners not to repair or replace any part unless the user’s manual recommends it NPE-2 User’s Information Manual, p. 6. The NPE-2 Installation & Operation Manual reserves gas connections and inlet gas pressure checks pp. 20, 24, venting p. 42 and the power connection p. 59 for licensed professionals, and gas type conversion for a qualified service agency p. 108.
If any vent pipe, elbow or intake pipe is damaged, separated at a joint, or shows corrosion, rust or melting, turn the heater off and stop using it NPE-2 User’s Information Manual, p. 5. For NPE-A2 and NPE-S2 heaters, Navien requires pre-authorization from its Technical Support for all repairs; your installer calls from the site NPE-2 Installation & Operation Manual, p. 145. The NPN user’s and installation manuals do not include this requirement.
Navien is a trademark of its owner. How House Works is not affiliated with or endorsed by Navien.
Sources
- Navien, Inc.. NPE-2 User's Information Manual. Version 1.0 (2020), part no. 20049624A. Accessed Oct 12, 2026.
- Navien, Inc.. NPN User's Information Manual. Version 1.0 (December 2020), part no. 20045995B. Accessed Oct 12, 2026.
- Navien, Inc.. NPE-2 Installation & Operation Manual. Version 2.0 (January 2026), part no. 20049624B; cover title: Installation Manual. Accessed Oct 12, 2026.
- Navien, Inc.. NPN Installation and Operation Manual. Version 1.0 (June 2021), part no. 20045995C; cover title: Installation Manual. Accessed Oct 12, 2026.
- Navien America Inc.. NR-21DU Remote Controller Manual. Part no. 20051848A (no version or date printed). Accessed Oct 12, 2026.