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Back to Navien NFB700-C Series

Navien NFB700-C Series troubleshooting and error codes

Use this table to identify what the visible code may mean and what information to share when scheduling service. Keep checks simple and visible; do not open electrical, refrigerant, gas, or sealed equipment compartments.

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Error-code table

Search codes for NFB700-C Series

Code Meaning System area Safe first step Action
E001 Heat exchanger overheat Equipment control Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E003 Ignition failure Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E004 False flame detection Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E012 Flame loss Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E016 Heat exchanger overheat Equipment control Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E030 Exhaust overheat Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E031 Burner overheat Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E046 Abnormal operation: heat exchanger limit or thermistor Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E047 Exhaust thermostat or thermistor open/short Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E060 Abnormal operation: dual venturi Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E109 Abnormal operation: fan motor Airflow / fan Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E110 Abnormal air pressure or exhaust blockage Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E127 Abnormal operation: air pressure sensor or air volume control Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E205 Heating supply temperature sensor Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E218 Heating return temperature sensor Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E278 External supply sensor not detected Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E279 External return sensor not detected Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E291 Return temperature exceeds supply temperature Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E302 Low water pressure Water flow / hydronics Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E352 High water pressure Water flow / hydronics Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E353 Water pressure sensor issue Temperature / sensor Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E480 Domestic hot water tank temperature sensor not detected Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E515 Abnormal operation: PCB Controls / communication Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E517 Abnormal operation: DIP switch setting Controls / communication Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E594 Abnormal operation: EEPROM Controls / communication Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E615 Abnormal operation: input and memory Controls / communication Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E736 Abnormal operation: cascade communication Controls / communication Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E740 Abnormal operation: outdoor temperature sensor Temperature / sensor Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E765 Abnormal external pump operation Water flow / hydronics Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E774 Manual reset limit Equipment control Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E775 Auto reset limit Equipment control Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E777 Low water cutoff activated Water flow / hydronics Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E782 Abnormal operation: front/main panel communication Controls / communication Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details
E784 Abnormal operation: zone controller communication Controls / communication Record the Navien code, check visible intake, exhaust, filter, thermostat, controller, and clearance conditions without opening panels, and schedule service if the condition remains. View details

Safety note

What is safe to check before service

These pages are meant to help document the issue, not replace diagnosis. GreenFlow should handle pressure-switch, electrical, refrigerant, lockout, recurring, and warranty-related conditions.

Safe visible checks

  • Thermostat display and settings
  • Filter condition and return-air path
  • Visible outdoor-unit obstruction
  • Photos of the code, unit, and nameplate

Stop and call

  • Repeated lockouts or recurring faults
  • Pressure-switch or sensor faults
  • Electrical odor, unusual noise, or ice buildup
  • Any sealed cabinet, refrigerant, gas, or warranty issue

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Jenny W.

Great service! On time, knowledgeable & professional

Michael C.

always available, easy to get a hold of, as a property manager I get lots no heat emergency, usually get to it same day or next day

Ray

Just had a service call because my tankless water heater stopped working with E110 code. Andrey located the root cause real quick and fixed the issue within half an hour, also gave reasonable recommendations for further maintenance.

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Andrey always does a great job.

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