Understanding Error Codes - Navien NFB-175H User's Information Manual

5.2 Understanding Error Codes

When an error code appears on the front panel, refer to the following chart for a definition and possible remedy
for the situation.
Error Code Reason
E001 Heat exchanger over temperature
E003 Ignition failure
E004 False flame detection
E012 Flame loss
E016 Overheating of heat exchanger
E030 Abnormal exhaust temperature
E031 Overheating of burner
E046 Abnormal operation: heat exchanger overheating sensor
E047 Abnormal operation: exhaust thermostat
E060 Abnormal operation: dual venturi
E109 Abnormal operation: fan motor
E110 Abnormal air pressure
E205 Abnormal operation: heating supply thermistor
E218 Abnormal operation: heating return thermistor
E278 Abnormal operation: system supply thermistor
E279 Abnormal operation: system return thermistor
E291 Supply/Return inversion limit
E302 Low water pressure
E352 High water pressure
E353 Abnormal operation: water pressure sensor
E480 Abnormal operation: water tank thermistor
E515 Abnormal operation: PCB component
E517 Abnormal operation: DIP switch setting
E594 Abnormal operation: EEPROM
E615 Abnormal operation: input and memory
E736 Abnormal operation: Cascade communication
Abnormal operation: outdoor temperature sensor
E740
(appears only when the outdoor reset curve is enabled).
E762 Abnormal flue gas duct: Vent pipe not properly inserted
E777 Abnormal operation: LWCO limit (external device)
E782 Abnormal operation: panel communication
Abnormal operation: zone controller communication
E784
(external device)
E786 Improper front panel
E788 Abnormal Gas Setting
If these remedies do not resolve the problem, contact Technical Support at 1-800-519-8794.
Self-diagnostic/Action
Auto reset/Manual reset
Manual reset
Auto reset
Manual reset
Manual reset
Auto reset/Manual reset
Manual reset
Auto reset
Auto reset/Manual reset
Alarm
Manual reset
Manual reset
Auto reset
Auto reset
Alarm
Alarm
Manual reset
Manual reset
Auto reset
Auto reset
Alarm
Alarm/Manual reset
Manual reset
Alarm
Alarm/Auto reset/Manual reset
Alarm
Alarm
Auto reset
Auto reset
Alarm
Alarm
Alarm
Manual reset (Start-up Wizard)
Troubleshooting 23