Green Flow Solution logo
Schedule Service

Product troubleshooting

Back to Navien NCB-H Series

Navien NCB-H 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.

Schedule Service +1 (857) 767-6414

Error-code table

Search codes for NCB-H 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
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
E351 Abnormal auto feeder valve 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
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
E407 Domestic hot water outlet thermistor open or short 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
E421 Cold water inlet thermistor open or short 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
E434 Abnormal operation: water adjustment valve 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
E439 Abnormal operation: flow sensor or no domestic water flow 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
E441 Domestic hot water inlet/outlet 2 sensor open or short 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
E445 Abnormal operation: bypass mixing valve 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
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
E761 Pump aquastat 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
E762 Vent pipe not properly inserted Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. View details
E773 Improper gas type or gas connection detected Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. 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
E786 Improper front panel or panel connection 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
E788 Incorrect gas type setting Combustion / venting Record the Navien code, avoid repeated reset attempts, and schedule GreenFlow service. 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

Brands We Service

Popular cities

Service Areas

Our Happy Customers

Anna G.

They quickly identified the issue with the heating system and fixed it efficiently. He explained everything clearly and made sure I understood what was going on. Very professional and reliable, extremely satisfied with the service.

Terry S.

Excellent service from best tech!

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.

Randy J.

Thanks to Andrey for an amazingly quick response to my request for a service call. He diagnosed and fixed my issue within 24 hours of my asking for help. Excellent service. Thanks.

View All