Short answer
Navien codes start with E. E003 means the burner did not light, E012 is flame loss, E016 and E030 are overheating often tied to a clogged inlet filter or scale, E110 is blocked venting, and E760 means a flush is due. Owners can check gas, power, filters and vents. Sensor and board codes need a pro.
Key facts
- Navien's NPE-2 manual lists E407 as the hot water outlet sensor fault and E515 as a main circuit board fault.[1]
- Navien's manual ties E016 (heat exchanger overheating) to a clogged cold water inlet filter or scale, both owner-level checks to start.[1]
- Navien technical support is listed in the NPE-2 manual at 1-800-519-8794.[1]
Before you use this table
If you smell gas, do not reset anything. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place[3].
This table covers the Navien NPE-2 condensing tankless line (NPE-180A2, 210A2 and 240A2, and the matching S2 models). The meanings are our paraphrase of the NPE-2 user's manual, not Navien's text[1]. For other Navien models, use the manual on Navien's downloads page[2].
"Power cycle once" means turning the unit off and back on one time. If the code returns, stop.
Navien NPE-2 code table
| Code | What it means | Safe homeowner check | Call a pro when |
|---|---|---|---|
| E003 | Ignition failure: the burner did not light | Main gas valve to the unit open; other gas appliances work; propane not empty | Still no light: gas pressure, igniter or flame rod |
| E004 | False flame: flame sensed when there should be none | Unit plugged into a properly grounded outlet | It returns: flame rod or board diagnosis |
| E012 | Flame lost after lighting | Clean the intake air filter per the manual; check the grounded outlet | It returns: gas supply or vent diagnosis |
| E016 | Heat exchanger overheating | Clean the cold water inlet filter; schedule a flush | It returns after both: descaling or sensor checks |
| E030 | Exhaust too hot; the unit shuts down above about 149 F flue temperature | Clean the inlet filter; schedule a flush | It returns: exhaust sensor and vent checks |
| E031 | Burner overheating | None | Always |
| E046 | High-limit safety tripped or abnormal | None | Always |
| E047 | Exhaust temperature sensor open or shorted | None | Always: sensor replacement |
| E060 | Dual venturi fault | None | Always |
| E109 | Fan motor fault | Clean the intake air filter | It returns: fan replacement |
| E110 | Abnormal air pressure: blocked exhaust or intake | Clear snow, nests or debris from the outside terminals; clean the intake filter | It returns: vent repair |
| E407 | Hot water outlet temperature sensor open or shorted | None | Always: sensor replacement |
| E421, E432, E441 | Other water temperature sensors open or shorted (cold inlet 1, cold inlet 2, hot water inlet 2) | None | Always |
| E434 | Water flow adjustment valve fault | None | Always |
| E438 | Circulation pump fault (pump or air handler setups) | Note whether the pump hums or vibrates, and tell the pro | Always |
| E439 | Flow sensor fault | None | Always |
| E445 | Bypass mixing valve fault | None | Always |
| E515 | Main circuit board fault | Confirm a grounded outlet; power cycle once | It returns: board replacement |
| E517 | DIP switch setting error | None | Always: installer settings need correcting |
| E593, E594, E615 | Front panel key, memory or input faults | Power cycle once | It returns |
| E736 | Cascade (multi-unit) communication fault | None | Always |
| E740 | Outdoor temperature sensor fault (air handler setups) | None | Always |
| E760 | Flushing or service reminder | Book a flush or routine service | n/a |
| E762 | Vent pipe not seated properly at the unit | Turn the unit off; do not run it | Always: a loose vent can leak exhaust |
| E773, E788 | Gas type mismatch: the unit or its settings do not match the gas supplied | None | Always: gas settings are licensed gas work |
| E782 | Main panel communication fault | None | Always |
| E785 | Flow switch or sensor fault (air handler setups) | None | Always |
Source: Navien NPE-2 User's Information Manual[1], paraphrased.
Myth: E515 is the outlet sensor
You will find websites that list E515 as the hot water outlet sensor. Navien's NPE-2 manual says otherwise: E407 is the outlet sensor, and E515 is the main circuit board[1]. A sensor and a board are very different parts and prices, so check the manual for your exact model before anyone orders parts.
The two filters that clear many Navien codes
Navien units have two owner-serviceable filters, and dirty ones show up behind several codes[1]:
- Cold water inlet filter. A clogged one restricts flow and can cause overheating codes (E016, E030).
- Intake air filter. A dirty one can cause flame loss and fan faults (E012, E109, E110).
The owner's manual shows how to reach and clean both. If either code returns after cleaning, call a pro.
Hard water and E760
E760 is a reminder, not a failure. Scale builds inside the heat exchanger over time, especially in hard water, and leads to overheating codes if it is ignored. HomeGuide's 2025 range for a tankless flush and descale is $75 to $300[4].
When to call a pro
- E762 (vent not seated) or E773 and E788 (gas type mismatch): turn the unit off.
- Any overheat code that returns after cleaning the inlet filter.
- Any sensor, valve, pump, fan or board code.
- E003 or E012 that returns with gas confirmed on.
More questions
What is the difference between Navien A2 and S2 models?
NPE-A2 models have a built-in buffer tank and recirculation pump; NPE-S2 models do not. Pump codes such as E438 mainly apply to A2 units or installs with an external recirculation pump.
Do Navien combi boilers use the same codes?
The NCB combi boilers share many codes for common parts like ignition, flame, sensors and fans, but add space-heating codes such as low system pressure. Use the NCB manual for those.
Sources
- NPE-2 User's Information Manual (EN, 2020-12 revision), Navien. Accessed 2026-10-06.
- NPE-A2 series downloads, Navien. Accessed 2026-10-06.
- What to do if you smell natural gas, CenterPoint Energy. Accessed 2026-10-06.
- Hot water heater repair cost (Aug 7, 2025), HomeGuide. Accessed 2026-10-06.
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