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ErrBase

Navien Waterheater Error Codes

All Navien waterheater error codes with step-by-step troubleshooting, multimeter specs, and OEM part numbers.

10 error codes

CodeMeaning
E001The unit failed to establish a flame on the first ignition attempt. E001 is an early-stage ignition fault that precedes E003, which fires after all 3 attempts fail.
highbeginner
E003After three ignition attempts with no flame signal detected, the PCB shuts down the sequence and throws a lockout. The gas valve, spark igniter, and flame rod sensor all have to work together at exactly the same moment for a successful light-off. Any one of them failing breaks the whole chain.
highintermediate
E012The burner flame lit up fine but went out while the unit was actively heating water. It's different from E003, which means ignition never happened at all. This one means you had a flame, lost it, and the rod stopped seeing the ionization signal it needs to keep the valve open.
highintermediate
E110The differential pressure switch detected that air isn't moving through the exhaust and intake pathways correctly. Either the path is physically blocked, or the pressure drop across the vent system is outside the range the switch is calibrated to accept.
highbeginner
E302The control board is picking up a flame signal from the flame rod even though the gas valve is closed and nothing should be burning. It's a safety lockout. The board won't let the unit run again until that false signal clears.
moderateintermediate
E762The outlet water temperature exceeded 190 degrees Fahrenheit (87.7 degrees Celsius), triggering a high-limit safety lockout. The unit shuts off to prevent scalding and thermal damage to components.
highintermediate
E773The exhaust gas temperature exceeded the safe thermal limit. A thermal fuse or high-limit sensor in the exhaust path tripped due to excessive heat, causing a safety lockout.
highintermediate
HUBYour Navien detected a fault condition and locked out to protect itself. The letter-number code on the display tells you exactly which system tripped. Each code maps to a specific sensor, circuit, or mechanical failure point inside the unit, so the display is basically the unit telling you where to look.
lowbeginner
NO-HOT-WATERThe control board detected a condition that prevents safe firing. Could be insufficient water flow through the heat exchanger, a failed ignition sequence, or a backed-up condensate drain tripping the safety float switch. The unit shuts itself down to prevent damage.
moderateintermediate
RESETGuide covering all three reset methods for Navien NPE and NCB series: soft reset via Info button, hard reset via power cycle, and factory reset via controller menu.
lowbeginner