Which models this covers
Navien NPE-2 condensing tankless water heaters: NPE-180, NPE-210 and NPE-240 (A2 and S2), from the NPE-2 User’s Information Manual. Older NPE-A/S (non-“2”) models may differ. Codes differ between control boards, so check the code chart printed on your unit or in its manual if your model isn’t listed.
How to read the code
The code shows on the front display. Press the Back button to reset after fixing the cause. If the code returns, follow the action below or contact Navien technical support.
Common error codes
| Code | What it means | What to do |
|---|---|---|
| E003 | Ignition failure | Make sure the main gas supply valve is fully open, then reset. |
| E004 | False flame detection | Check that the power cord is plugged into a properly grounded outlet. |
| E012 | Flame loss | Clean the intake air filter and check grounding. |
| E016 | Heat exchanger overheating | Clean the inlet water filter and flush (descale) the heat exchanger. |
| E030 | Exhaust overheating (above 149°F / 65°C) | Clean the inlet water filter and flush the heat exchanger. |
| E109 | Fan motor problem | Clean the intake air filter. If it returns, call a pro.Pro |
| E110 | Abnormal air pressure | Make sure the exhaust and intake aren’t blocked, and clean the intake filter. |
| E407 | Hot water outlet thermistor open or shorted | Call a pro or Navien technical support.Pro |
| E438 | Recirculation pump problem | Check the pump. If unsure, call a pro.Pro |
| E515 | Control board (PCB) abnormal | Check grounding. If it returns, call a pro.Pro |
| E760 | Flushing / service alarm | Schedule descaling service with your installer. |
| E788 | Gas type setting mismatch | Call a pro to match the gas DIP switch setting.Pro |
| Other codes | E031, E046, E047, E060, E421, E432, E434, E439, E441, E445, E517, E593, E594, E615, E736, E740, E762, E773, E782, E785 | Contact Navien technical support or a pro.Pro |
Sources
These codes are transcribed from the manufacturer’s own documentation. Many websites repeat codes that don’t match the manuals, so when in doubt, trust the chart on your unit.
Code pointing to a big repair? Check whether to repair or replace before you pay for it.
Frequently asked questions
What does E003 mean on a Navien?
E003 is an ignition failure. Navien’s first step is to make sure the main gas valve to the heater is fully open. Gas supply problems, including an undersized gas line, are common causes. Reset with the Back button.
What does E407 mean on a Navien tankless?
Per Navien’s manual, E407 means the hot water outlet thermistor (temperature sensor) is open or shorted. That’s a part replacement, so contact a pro or Navien technical support. Some websites wrongly call it a low-pressure code.
How do I reset a Navien tankless water heater?
Fix the underlying cause first, then press the Back button on the front panel to clear the code. If the code returns, follow the action in the table or contact technical support.