Error Code	Symptom	Fault Type	Guide
E001	Navien furnace will not fire, display shows E001, burner never lights	Low Water Pressure / Flow Fault	View Details
E002	Navien furnace locks out with E002, unit attempts to start but shuts down quickly	Low Water Level / Flow Switch Fault	View Details
E003	Navien furnace shows E003 and will not ignite, fan may run briefly then stop	Ignition Failure / Flame Not Detected	View Details
E004	Navien furnace displays E004, unit shuts down shortly after ignition attempt	Flame Loss During Operation	View Details
E010	Navien furnace shows E010 and shuts down, fan may run at high speed	Abnormal Air Pressure / Fan Motor Fault	View Details
E012	Navien furnace displays E012, unit will not run, sometimes after heavy rain or snow	Flue Blockage / Exhaust Restriction	View Details
E016	Navien furnace shows E016 and shuts down during operation, often after running for a while	Overheating / High Limit Trip	View Details
E021	Navien furnace displays E021, unit will not start heating cycle	Thermistor (Temperature Sensor) Fault	View Details
E022	Navien furnace shows E022, unit may start but quickly shuts down	Return Water Thermistor Fault	View Details
E027	Navien furnace intermittently shuts down with E027, especially during long runs	Exhaust Overheat / Flue Gas Temperature Fault	View Details
E030	Navien furnace shows E030 and will not operate, often after power issues	Internal Control Communication Error	View Details
E046	Navien furnace displays E046, unit may run at reduced capacity or shut down	Outdoor Temperature Sensor Fault (for systems using outdoor reset)	View Details
E051	Navien furnace shows E051, heating demand not recognized or unit does not respond to thermostat	Thermostat / Room Controller Communication Fault	View Details
E060	Navien furnace displays E060, unit may not modulate correctly or may shut down	Gas Valve Modulation / Valve Drive Fault	View Details
E109	Navien furnace shows E109, unit may not start or may shut down unexpectedly	Internal Fan / Blower Speed Feedback Fault	View Details
E110	Navien furnace displays E110, unit locks out and will not restart	Flame Detection Circuit Fault	View Details
E127	Navien furnace intermittently shows E127, especially during very cold weather	Condensate Drain / Trap Fault	View Details
E203	Navien furnace shows E203, unit does not respond to zone calls properly	Zone Control / Internal Pump Control Fault	View Details
E302	Navien furnace displays E302, unit may not start after power outage	EEPROM / Configuration Data Error	View Details
–	Navien furnace cabinet vibrates excessively during operation	Mechanical Vibration / Imbalanced Fan	View Details
–	Navien furnace display is blank and unit is completely unresponsive	No Power / Control Failure	View Details
–	Navien furnace display shows fluctuating or incorrect water temperature readings	Erratic Temperature Sensing	View Details
–	Navien furnace display shows normal operation but house is overheating	Overheating Space / Control Misconfiguration	View Details
–	Navien furnace emits a strong exhaust or burning smell near the unit or vent termination	Combustion Odor / Incomplete Combustion	View Details
–	Navien furnace fan runs but burner does not light and no error code is displayed	No Heat / Ignition Sequence Not Completing	View Details
–	Navien furnace frequently loses pressure and requires frequent refilling	Chronic Pressure Loss / System Leak	View Details
–	Navien furnace frequently trips the household breaker	Electrical Overload / Short Circuit	View Details
–	Navien furnace is very noisy during operation, with rumbling or roaring sounds from the burner area	Combustion Noise / Burner Instability	View Details
–	Navien furnace locks out occasionally during very cold weather without a clear error code, outdoor unit or piping appears frosted	Freeze Protection / Low Temperature Lockout	View Details
–	Navien furnace makes loud banging or knocking noises in the piping when the burner fires or shuts off	Water Hammer / Thermal Expansion Noise	View Details
–	Navien furnace produces gurgling or trickling water sounds inside the unit	Air in Heat Exchanger / Condensate Flow Noise	View Details
–	Navien furnace runs but does not provide enough heat to the home; supply water temperature is lower than expected	Underheating / Insufficient BTU Output	View Details
–	Navien furnace runs but some zones or radiators stay cold	Zone Flow Imbalance / Airbound Zones	View Details
–	Navien furnace short cycles: frequently turns on and off with very short run times	Short Cycling / Oversized Boiler or Control Misconfiguration	View Details
–	Water leaking from the bottom of the Navien furnace cabinet	Internal Water Leak	View Details

Navien Furnaces Error Codes

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