Navien error codes on an NPE-A2 or NPE-S2 tankless water heater start with an E and three digits. The one people search most, E003, is an ignition failure, and the first thing Navien tells you to check is that the gas valve is open. The full list of Navien tankless water heater troubleshooting codes is below, with Navien’s own owner steps. A repair starts with our $99 diagnostic; a new tankless water heater is $8,886 to $10,486 installed in Northern Virginia. From about $148 a month at 0% APR for 60 months, the whole price financed, on approved credit.
Our Navien tankless repair page covers what usually breaks and what it costs.
| Code | What it means | What to do |
|---|---|---|
| E003 | Ignition failure | Make sure the main gas valve is open; then call |
| E004 | False flame detection | Check the power cord is properly grounded |
| E012 | Flame loss | Clean the intake air filter; check the cord is grounded |
| E016 | Heat exchanger overheating | Clean the cold water inlet filter; flush the heat exchanger |
| E030 | Exhaust overheating | Clean the inlet filter; flush the heat exchanger |
| E047 | Exhaust temperature sensor open or shorted | Call: a sensor |
| E109 | Fan motor not running right | Clean the intake air filter |
| E110 | Abnormal air pressure | Clear the exhaust pipe; clean the intake air filter |
| E407 | Hot water outlet sensor open or shorted | Call: a sensor |
| E439 | Flow sensor fault | Call |
| E515 | Control board fault | Check the cord is grounded; then call |
| E760 | Flushing or service alarm | It’s due for a flush |
| E762 | Vent pipe not properly inserted | Call |
| E773 | Running on the wrong gas | Call |
From Navien’s NPE-2 user’s information manual. To reset after you’ve fixed the cause, press the Back button on the front panel.
The two filters that clear half these codes
The intake air filter (E012, E109, E110) clogs with dust and lint; Navien says to clean it every 3 to 4 months. The cold water inlet filter (E016, E030) catches grit and scale. Both are a few minutes with the unit off and the water shut off at the heater.
Scale is what kills tankless water heaters
Navien’s own words: scale from hard water is the biggest single reason its units fail. Its manual recommends a softener or its PeakFlow system once water is harder than 4 grains per gallon, and a yearly heat exchanger flush in a home with no treatment. E016, E030 and the E760 service alarm are all scale talking. Navien’s warranty doesn’t cover hard water deposits or skipped maintenance, so the flush is also how you keep the warranty.
On a combi that heats the house too, E777 is the low water cutoff: the heating loop needs water, and Navien says the cold fill pressure must be at least 12 psi. E352 is high water pressure on the heating side. E110 there reads as an exhaust blockage (NCB-H manual).
No code, no hot water
Navien says the likely cause is the flow sensor not spinning, often from debris. Clean the inlet filter first. If you’ve lost power, remember freeze protection needs electricity, and Navien doesn’t cover freeze damage.
Ignition failure: the burner didn’t light. Check the gas valve to the heater is fully open and, on propane, that the tank isn’t empty. If it comes back, call. The diagnostic is $99.
Fix the cause first, then press the Back button on the front panel. A code that returns right away is a call.
Navien’s flushing and service alarm. It’s due for maintenance, usually a heat exchanger flush.
Navien’s manual says once a year in a home when the water is harder than 4 grains per gallon and there’s no softener or PeakFlow treatment. We flush them; see the Navien repair page.
