Navien tankless water heater error codes
Navien's NPE line is one of the most widely installed condensing tankless ranges in the US. Its codes are numbered E003 through E788 — a different scheme from every other brand here — and the table grew between generations: the current NPE-2 units report faults the original NPE has no code for at all, including using the wrong gas and a vent pipe that was never seated properly.
Pick your series below — Navien code meanings are documented per series, because the same number can point to a different fault on a different generation.
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NPE-2
32 documented codes
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NPE-A / NPE-S
27 documented codes
Codes documented on more than one Navien series
Pick a number to see what it means on each series side by side — useful when you know the code but not the generation.
Not sure which series you own? The model-number decoder matches the number on your rating label to the right table.
All Navien codes in one table
| Code | Series | Error | Verdict |
|---|---|---|---|
| E003 | NPE-2 | Ignition failure | Call a pro |
| E004 | NPE-2 | False flame detection | Call a pro |
| E012 | NPE-2 | Flame loss | Call a pro |
| E016 | NPE-2 | Overheating of heat exchanger | Call a pro |
| E030 | NPE-2 | Exhaust overheating | Call a pro |
| E031 | NPE-2 | Overheating of burner | Call a pro |
| E046 | NPE-2 | Limit control fault | Call a pro |
| E047 | NPE-2 | Exhaust thermostat: open or short circuit | Call a pro |
| E060 | NPE-2 | Dual venturi fault | Call a pro |
| E109 | NPE-2 | Fan motor fault | Call a pro |
| E110 | NPE-2 | Abnormal air pressure | Call a pro |
| E407 | NPE-2 | Hot water outlet thermistor: open or short circuit | Part replacement |
| E421 | NPE-2 | Cold water inlet thermistor 1: open or short circuit | Part replacement |
| E432 | NPE-2 | Cold water inlet thermistor 2: open or short circuit | Part replacement |
| E434 | NPE-2 | Water adjustment valve fault | Part replacement |
| E438 | NPE-2 | Circulation pump fault | Part replacement |
| E439 | NPE-2 | Flow sensor fault | Part replacement |
| E441 | NPE-2 | Hot water inlet thermistor 2: open or short circuit | Part replacement |
| E445 | NPE-2 | Bypass mixing valve fault | Part replacement |
| E515 | NPE-2 | PCB fault | Call a pro |
| E517 | NPE-2 | DIP switch setting fault | Call a pro |
| E593 | NPE-2 | Front panel key fault | Part replacement |
| E594 | NPE-2 | EEPROM fault | Call a pro |
| E615 | NPE-2 | Input and memory fault | Call a pro |
| E736 | NPE-2 | Cascade communication fault | Call a pro |
| E740 | NPE-2 | Outdoor temperature sensor fault | Part replacement |
| E760 | NPE-2 | Flushing / service alarm | DIY fix |
| E762 | NPE-2 | Vent pipe not properly inserted | Call a pro |
| E773 | NPE-2 | Using the wrong gas | Call a pro |
| E782 | NPE-2 | Main panel communication fault | Call a pro |
| E785 | NPE-2 | Flow switch or flow sensor fault | Part replacement |
| E788 | NPE-2 | Gas type setting does not match the panel | Call a pro |
| E003 | NPE-A / NPE-S | Ignition failure | Call a pro |
| E004 | NPE-A / NPE-S | False flame detection | Call a pro |
| E012 | NPE-A / NPE-S | Flame loss | Call a pro |
| E016 | NPE-A / NPE-S | Overheating of heat exchanger | Call a pro |
| E030 | NPE-A / NPE-S | Exhaust overheating | Call a pro |
| E046 | NPE-A / NPE-S | Limit control fault | Call a pro |
| E047 | NPE-A / NPE-S | Exhaust thermostat fault | Call a pro |
| E060 | NPE-A / NPE-S | Dual venturi fault | Call a pro |
| E109 | NPE-A / NPE-S | Fan motor fault | Call a pro |
| E110 | NPE-A / NPE-S | Abnormal air pressure | Call a pro |
| E407 | NPE-A / NPE-S | Hot water outlet thermistor: open or short circuit | Part replacement |
| E421 | NPE-A / NPE-S | Cold water inlet thermistor 1: open or short circuit | Part replacement |
| E432 | NPE-A / NPE-S | Cold water inlet thermistor 2: open or short circuit | Part replacement |
| E434 | NPE-A / NPE-S | Water adjustment valve fault | Part replacement |
| E438 | NPE-A / NPE-S | Circulation pump fault | Part replacement |
| E439 | NPE-A / NPE-S | Flow sensor fault | Part replacement |
| E441 | NPE-A / NPE-S | Hot water inlet thermistor 2: open or short circuit | Part replacement |
| E445 | NPE-A / NPE-S | Bypass mixing valve fault | Part replacement |
| E515 | NPE-A / NPE-S | PCB fault | Call a pro |
| E517 | NPE-A / NPE-S | DIP switch setting fault | Call a pro |
| E593 | NPE-A / NPE-S | Front panel key fault | Part replacement |
| E615 | NPE-A / NPE-S | Input and memory fault | Call a pro |
| E736 | NPE-A / NPE-S | Cascade communication fault | Call a pro |
| E740 | NPE-A / NPE-S | Outdoor temperature sensor fault | Part replacement |
| E760 | NPE-A / NPE-S | Flushing / service alarm | DIY fix |
| E782 | NPE-A / NPE-S | Main panel communication fault | Call a pro |
| E785 | NPE-A / NPE-S | Flow switch or flow sensor fault | Part replacement |
Each code links to a full page: what the manual says for that exact series, the likely fix, and what it should cost.