Navien · Error codes
Navien error codes and alerts
Identical code numbers can mean different things on different controllers, so every entry is tied to the documented series, controller and manual version. A code is never a diagnosis.
If you smell gas
- Stop what you are doing. Do not use phones, switches, matches or anything that can spark inside.
- Go outside and leave the door open behind you.
- Call the FortisBC 24-hour emergency line at 1-800-663-9911 or dial 911.
Only after that, call ROMA about the boiler. Official guidance: FortisBC gas leaks and odour.
Navien NCB-H combi boilers (front-panel display, NCB-H manual error codes)
E001
Heat exchanger overheat. The control displays E001 when the space heating water temperature at the heat exchanger outlet thermistor rises ab…
Details
E003
Ignition failure. In the case of an ignition failure the boiler attempts ignition ten times, and if no flame is detected the system displays…
Lockout
E004
False flame. A flame signal detected continuously for three seconds before combustion or during post-purge while fuel supply is stopped trig…
Lockout
E012
Flame loss. When the system detects loss of flame during combustion it stops the fuel supply and attempts to restart, and displays this manu…
Lockout
E016
Heat exchanger overheat. The overheat controller on the heat exchanger was initiated during combustion or standby, switching the boiler into…
Details
E030
Exhaust overheat. The exhaust overheat controller on the exhaust duct trips when the temperature exceeds 230 °F (110 °C) for ten minutes or …
Details
E031
Burner overheat. The boiler detected an overheating of the burner, and the manual directs contacting technical support to diagnose this abno…
Details
E046
Heat exchanger thermistor. The control detected abnormal operation of the heat exchanger thermistor or its limit control, so the thermistor …
Details
E047
Exhaust thermistor. The control detected abnormal operation of the exhaust thermostat, so check the exhaust thermistor, whose normal resista…
Details
E060
Abnormal dual venturi. This error is displayed when the wiring is disconnected or the Dual Venturi malfunctions, and the boiler switches int…
Details
E109
Abnormal fan motor. The system detected a fan motor RPM signal that stayed low or close to zero after the fan started or for three seconds d…
Details
E110
Exhaust blockage. The boiler senses the air volume and RPM signal and displays this error when the initial fan auto-adjust was not performed…
Details
E205
Heating supply temperature sensor. The control detected an open or short circuited heating supply thermistor, such as a heat exchanger outpu…
Details
E218
Heating return temperature sensor. The control detected an open or short circuited heating return thermistor, such as a heat exchanger input…
Details
E278
External supply sensor not detected. The control reported abnormal operation of the system supply thermistor because the external supply tem…
Details
E279
External return sensor not detected. The control reported abnormal operation of the system return thermistor because the external return tem…
Details
E302
Low water pressure. The control detected low water pressure in the space heating system, and the low water pressure error is cleared by an a…
Details
E351
Abnormal auto feeder valve. When the system pressure is lower than 7.3 psi (0.5 bar) the boiler stops operation and refills automatically, a…
Details
E352
High water pressure. The water pressure sensor reported a high water pressure of 56.6 psi or higher continuing for three seconds, and the er…
Details
E353
Water pressure sensor. The control detected an error in the water pressure sensor output below 0.3 V or above 2.8 V continuously for three s…
Details
E407
Domestic hot water outlet sensor. The control detected that the domestic hot water outlet thermistor at the DHW outlet elbow is open or shor…
Details
E421
Domestic cold water inlet sensor. The control detected that the domestic cold water inlet thermistor is open or short circuited, such as a t…
Details
E434
Abnormal water adjustment valve. The control reported abnormal operation of the water adjustment valve in the DHW system, an alarm condition…
Details
E439
No domestic water flow detected. When no flow is detected during DHW operation in a cascade system, the control considers the flow sensor de…
Details
E441
Domestic hot water outlet 2 sensor. The control detected that the second domestic hot water outlet thermistor is open or short circuited, an…
Details
E445
Abnormal bypass mixing valve. The control reported abnormal operation of the bypass mixing valve in the DHW system, an alarm condition that …
Details
E515
Abnormal PCB. An error in the internal circuit of the PCB, such as a resistance, transistor or relay fault, displays this manually cleared e…
Details
E517
Abnormal DIP switch. The DIP switches on the PCB are not set to their proper positions, so the switches must be changed to the correct setti…
Details
E594
Abnormal EEPROM. Communication is abnormal in parts of the PCB, so the unit should be reset and the main PCB replaced if the E594 error cont…
Details
E615
Abnormal memory. The PCB received an abnormal signal input, so turn the power reset switch off and on and replace the main PCB if the error …
Details
E736
Cascade communication. The control detected abnormal operation of the cascade communication between the linked boilers, an alarm condition t…
Details
E740
Outdoor sensor not detected. When the outdoor sensor reads below 2.2kΩ or above 122.2kΩ continuously for three seconds, the boiler displays …
Details
E761
Pump aquastat not detected. The control reported abnormal operation of the Pre-Heat Aquastat because the pump aquastat was not detected, so …
Details
E762
Vent pipe not fully inserted. The control detected an abnormal flue gas duct condition because the vent pipe is not properly inserted, and t…
Details
E773
Improper gas type detected. The control detected that the boiler is using the wrong gas, an installation error that is resolved with a param…
Details
E777
Low water cutoff activated. The external low water cutoff device, which has the service code 7700, signalled activation, so check the LWCO w…
Details
E782
Front panel communication. The control reported abnormal operation of main panel communication, so check the wiring between the front panel …
Details
E784
Zone controller communication. The control reported abnormal operation of the zone controller communication, an alarm condition that the man…
Details
E786
Improper front panel. The control detected that the front panel installed on the boiler is improper, an alarm condition that the manual dire…
Details
E788
Incorrect gas type setting. The gas type setting is abnormal, so check the supplied gas type and match the gas type setting on the PCB DIP s…
Details
Navien NFB-H boilers (front-panel display, NFB-H manual error codes)
E001
Heat exchanger overheat. The control displays E001 when the space heating water temperature stays above 210 °F to prevent boiling in the hea…
Details
E003
Ignition failure. The boiler attempts ignition ten times, and when no flame is detected it displays this error, which must be manually clear…
Lockout
E004
False flame. A flame signal detected continuously for three seconds while combustion should not be running triggers this automatically clear…
Lockout
E012
Flame loss. When flame loss during combustion occurs twenty times consecutively despite restart attempts, the system displays this manually …
Lockout
E016
Heat exchanger overheat. The bimetal overheat controller on the heat exchanger switched the boiler into lock-out, post-purge and pump operat…
Details
E030
Exhaust overheat. The exhaust overheat controller shuts down the unit when the flue temperature exceeds 230 °F (110 °C) for more than ten mi…
Details
E031
Burner overheat. When the burner overheating prevention fuse opens for one second or longer, the control locks the boiler out and the fuse m…
Details
E046
Heat exchanger thermistor. The control detected a fault in the heat exchanger thermistor or its high limit switch circuit, so check the swit…
Details
E047
Exhaust thermistor. The control detected an open or shorted exhaust thermistor, so check the thermistor connection and its connection to the…
Details
E060
Abnormal dual venturi. The Dual Venturi wiring is disconnected or the component malfunctions, so the boiler locks out until the venturi wiri…
Details
E109
Abnormal fan motor. The system detected a fan motor RPM signal that remained low or near zero and switched the boiler into lock-out for a fa…
Details
E110
Exhaust blockage. The boiler senses airflow and fan RPM and shows this error when fan auto-adjust was not performed or the air pressure stay…
Details
E205
Heating supply temperature sensor. The control detected an open or shorted heating supply thermistor, for example an open reading of 14 °F (…
Details
E218
Heating return temperature sensor. The control detected an open or shorted heating return thermistor and initiates a boiler shutdown until t…
Details
E278
External supply sensor not detected. The control detected an open or short in the system supply temperature sensor and shuts the boiler down…
Details
E279
External return sensor not detected. The control detected an open or short in the system return temperature sensor and shuts the boiler down…
Details
E291
Return temperature exceeds supply. The system stops operation when the return temperature rises more than 10 °F (5.5 °C) above the supply te…
Details
E302
Low water pressure. The water pressure sensor detected pressure below the low pressure standard for more than three seconds, so check for wa…
Details
E352
High water pressure. The water pressure sensor detected pressure above the high pressure standard for more than three seconds and stopped op…
Details
E353
Water pressure sensor. The control detected the water pressure sensor output below 0.3 V or above 2.8 V continuously for three seconds and i…
Details
E480
DHW tank sensor not detected. The control did not detect the domestic hot water tank sensor, so check the sensor connections for a proper si…
Details
E515
Abnormal PCB. An internal PCB circuit fault or a communication failure between the PCB and components such as the igniter, fan, or dual vent…
Lockout
E517
Abnormal DIP switch. The DIP switch settings on the PCB are not set correctly, so change the switches to the proper settings and reset the u…
Details
E594
Abnormal EEPROM. Communication within parts of the PCB became abnormal, so reset the unit and replace the main PCB if the E594 display conti…
Details
E615
Abnormal memory. The PCB received abnormal signal inputs from components such as the heat exchanger high limit switch or the flame rod, indi…
Lockout
E736
Cascade communication. The boiler could not communicate with the cascade system, so check the cascade wiring connection and the PCB.…
Details
E740
Outdoor sensor not detected. When the outdoor sensor reads out of range for three seconds and the outdoor reset curve is enabled, the boiler…
Details
E762
Vent pipe not fully inserted. The vent switch detected that the vent pipes are not properly installed or seated, so insert the exhaust pipe …
Details
E777
Low water cutoff activated. The external low water cutoff device signalled an open condition for more than five seconds, so check the system…
Details
E782
Front panel communication. The boiler PCB could not communicate with the front panel, so check the wiring connection between the panel and t…
Details
E784
Zone controller communication. The boiler PCB could not communicate with the zone controller, so check the zone controller wiring connection…
Details
E786
Improper front panel detected. The control detected that the installed front panel is improper or an incorrect version, so check that the co…
Details
E788
Incorrect gas type setting. The gas type set on the panel DIP switch does not match the supplied gas type, so correct the gas type setting o…
Details
Navien NFC-H fire-tube combi boilers (front-panel display, NFC-H manual error codes)
E001
Heat exchanger over temperature. The control displays E001 to prevent boiling when the space heating water temperature stays above 210 °F, a…
Details
E003
Ignition failure. The boiler attempts ignition ten times, and when no flame is detected the system displays this error on the front panel to…
Lockout
E004
False flame detection. A flame signal detected continuously for three seconds before combustion or during post-purge displays this false-fla…
Lockout
E012
Flame loss. When flame loss is detected during combustion the system stops the fuel supply and restarts, displaying this manually cleared er…
Lockout
E016
Overheating of heat exchanger. The heat exchanger overheat controller was initiated during combustion or standby, locking the boiler out whi…
Details
E030
Abnormal exhaust temperature. The exhaust overheat controller shuts the unit down when the flue temperature exceeds 230 °F (110 °C) for ten …
Details
E031
Overheating of burner. When the burner overheating prevention fuse has been opened, overheating of the burner occurs and the burner and temp…
Details
E046
Abnormal operation: heat exchanger overheating sensor. The control detected abnormal operation of the heat exchanger overheating sensor, so …
Details
E047
Abnormal operation: exhaust thermostat. The control detected an open or shorted exhaust thermistor, whose normal resistance between pins 1 a…
Details
E060
Abnormal operation: dual venturi. This error displays when the Dual Venturi wiring is disconnected or the component malfunctions, and the bo…
Details
E109
Abnormal operation: fan motor. The system checks the fan RPM signal and locks out the boiler when the RPM stays low or close to zero after t…
Details
E110
Abnormal air pressure. The boiler senses the air volume and RPM signal and displays this error when the initial fan auto-adjust was not perf…
Details
E205
Abnormal operation: heating supply thermistor. An open error of 14 °F (-10 °C) or lower in the heat exchanger output temperature sensor disp…
Details
E218
Abnormal operation: heating return thermistor. The control detected an open circuit error in the heat exchanger input temperature sensor, wh…
Details
E278
Abnormal operation: system supply thermistor. An open circuit error in the system supply temperature sensor displays this code and initiates…
Details
E279
Abnormal operation: system return thermistor. An open circuit error in the system return temperature sensor displays this code and initiates…
Details
E351
Abnormal auto feeder valve (make-up water). The auto feeder valve is abnormal, so check for leaks inside the boiler, the direct water supply…
Details
E352
High water pressure. The boiler stops operation when the water pressure sensor detects pressure above the standard for more than three conse…
Details
E353
Abnormal operation: water pressure sensor. The water pressure sensor output below 0.3 V or above 2.8 V detected continuously for three secon…
Details
E407
Hot water outlet: thermistor open or short circuit. The control detected a disconnection or short circuit in the hot water outlet 1 temperat…
Details
E421
Cold water inlet: thermistor open or short circuit. The control detected a disconnection or short circuit in the cold water intake temperatu…
Details
E434
Abnormal operation: water adjustment valve. The water adjustment valve is abnormal, so check its harness when no feedback signal is received…
Details
E439
Abnormal operation: flow sensor. The control detected abnormal operation of the flow sensor, so check the water adjust valve harness for deb…
Details
E441
Hot water outlet 2: thermistor open or short circuit. The control detected a disconnection in the harness of the hot water outlet 2 temperat…
Details
E445
Abnormal operation: bypass mixing valve. The bypass mixing valve is abnormal, so check its harness for disconnections when there is no feedb…
Details
E515
Abnormal operation: PCB component. An error in the internal circuit of the PCB, such as a resistance, transistor, or relay fault, displays t…
Details
E517
Abnormal operation: DIP switch setting. The DIP switches on the PCB are not set to the proper positions, so change them to the correct setti…
Details
E594
Abnormal operation: EEPROM. Communication became abnormal in parts of the PCB, so reset the unit and replace the main PCB if the E594 error …
Details
E615
Abnormal operation: input and memory. The PCB received an abnormal signal input, so turn the power reset switch off and on and replace the m…
Details
E736
Abnormal operation: cascade communication. The boiler detected abnormal cascade communication, so check the cascade wiring connection and ch…
Details
E740
Abnormal operation: outdoor temperature sensor. When the outdoor sensor reads below 2.2kΩ or above 122.2kΩ for three seconds, the boiler cha…
Details
E761
Abnormal operation: Pre-Heat Aquastat. The Pre-Heat Aquastat is abnormal, so check the aquastat cables, change the aquastat, or select a dif…
Details
E762
Abnormal flue gas duct: vent pipe not properly inserted. The vent pipe is not properly inserted, so check that the vent pipes are properly i…
Details
E773
Using the wrong gas. The boiler is operating on the wrong gas, so check the gas conversion to ensure it matches the gas type being supplied.…
Details
E777
Abnormal operation: LWCO limit (external device). When the LWCO signal is detected as open for more than five seconds, the system determines…
Lockout
E782
Abnormal operation: panel communication. Communication between the main control and the front panel is abnormal, so check that the wiring fr…
Details
E784
Abnormal operation: zone controller communication. The control detected abnormal communication with the zone controller, so check the zone c…
Details
E786
Improper front panel. The control detected that the front panel is improper, so check the front panel and verify that the correct panel vers…
Details
E788
Abnormal gas setting. The gas type setting is abnormal, so check the supplied gas type and match it to the gas type setting on the PCB DIP s…
Details
Navien NHB-H compact boilers (front-panel display, NHB-H manual error codes)
E001
Heat Exchanger Overheat. The boiler displays E001 when the space heating water temperature at the heat exchanger outlet thermistor is higher…
Details
E003
Ignition Failure. E003 appears after the boiler attempts ignition ten times without detecting a flame, and typical causes relate to the gas …
Lockout
E004
False Flame. E004 appears when a flame signal is detected continuously for three seconds before combustion or during post-purge while the fu…
Lockout
E012
Flame Loss. E012 appears when the system detects loss of flame during combustion, stops supplying fuel, attempts to restart, and counts twen…
Lockout
E016
Heat Exchanger Overheat. E016 displays when the overheat controller on the heat exchanger is initiated during combustion or standby, and the…
Details
E030
Exhaust Overheat. E030 displays when the overheat controller on top of the exhaust duct initiates after the exhaust temperature exceeds 230°…
Details
E046
Heat Exchanger Thermistor. E046 indicates a problem with the heat exchanger thermistor, and the manual directs checking the connector, verif…
Details
E047
Exhaust Thermistor. E047 indicates that the exhaust thermistor is not operating normally, and the manual directs checking the connector, whe…
Details
E060
Abnormal Dual Venturi. E060 displays when the dual venturi malfunctions or its wiring is disconnected, and the boiler switches into lock-out…
Details
E109
Abnormal Fan Motor. E109 displays when the fan RPM signal stays low or near zero after the fan starts to run or is detected for three second…
Details
E110
Exhaust Blockage. E110 displays when the initial fan auto-adjust has not been performed or when the air pressure sensor reading is not up to…
Details
E205
Heating Supply Temp. Sensor. E205 displays when an open circuit error of 14°F (-10°C) or lower is detected in the heat exchanger output temp…
Details
E218
Heating Return Temp. Sensor. E218 displays when an open circuit error of 14°F (-10°C) or lower is detected in the heat exchanger input tempe…
Details
E278
Ext. Supply Sensor Not Detected. E278 indicates that the external supply temperature sensor is not detected, and the remedy listed in the er…
Details
E279
Ext. Return Sensor Not Detected. E279 indicates that the external return temperature sensor is not detected, and the remedy listed in the er…
Details
E291
Return Temp. Exceeds Supply. E291 indicates that the return water temperature exceeds the supply water temperature, and the remedy listed in…
Details
E302
Low Water Pressure. E302 indicates that the system water pressure is too low, and the remedy listed in the error chart is to check the water…
Details
E352
High Water Pressure. E352 displays when the water pressure sensor reports a level of 56.6 psi or higher that continues for three seconds, an…
Details
E353
Water Pressure Sensor. E353 displays when an error in the water pressure sensor of under 0.3V or over 2.8V is detected continuously for thre…
Details
E407
Hot water outlet thermistor open or short. E407 displays when an error in the DHW outlet elbow temperature sensor is detected as an open cir…
Details
E421
Cold water inlet thermistor open or short. E421 displays when the cold water inlet thermistor is open or short, so check whether the cold wa…
Details
E480
DHW Tank Sensor Not Detected. E480 indicates that the domestic hot water tank sensor is not detected, and the remedy listed in the error cha…
Details
E515
Abnormal PCB. E515 displays when an error occurs in the internal circuit of the PCB, such as a fault of a resistance, transistor, or relay. …
Details
E517
Abnormal DIP Switch. E517 indicates that the DIP switches on the PCB are not properly set, and the manual directs changing the DIP switches …
Details
E594
Abnormal EEPROM. E594 displays when communication between parts of the PCB is abnormal, and the manual directs resetting the unit and replac…
Details
E615
Abnormal Memory. E615 displays when the PCB receives an abnormal signal input, and the manual directs turning the power reset switch off and…
Details
E736
Cascade Communication. E736 indicates a cascade communication error, and the remedy listed in the error chart is to check the cascade cable.…
Details
E740
Outdoor Sensor Not Detected. E740 displays when an outdoor sensor error of under 2.2kΩ or over 122.2kΩ is detected continuously for three se…
Details
E762
Vent Pipe Not Fully Inserted. E762 indicates that the vent pipe is not fully inserted, and the remedy is to insert the pipe 2-3/4 in. (70 mm…
Details
E777
Low Water Cutoff Activated. E777 indicates that the low water cutoff has been activated, and the manual directs checking whether the LWCO is…
Details
E782
Front Panel Communication. E782 indicates a front panel communication error, and the manual directs verifying that the wiring from the front…
Details
E784
Zone Controller Communication. E784 indicates a zone controller communication error, and the remedy listed in the error chart is to check th…
Details
E786
Improper Front Panel Detected. E786 indicates that an improper front panel has been detected, and the remedy listed in the error chart is to…
Details
E788
Incorrect Gas Type Setting. E788 indicates that the gas type setting is incorrect, and the remedy listed in the error chart is to check the …
Details
Navien NFB-C commercial boilers (front-panel display, NFB-C manual error codes)
E001
Heat exchanger overheat. E001 appears when the space heating water temperature rises above 216 °F (102 °C) to prevent boiling in the heat ex…
Details
E003
Ignition failure. The boiler attempts ignition ten times and, when no flame is detected, displays this error which must be manually cleared,…
Lockout
E004
False flame detection. A flame signal detected continuously for three seconds before combustion or during post-purge triggers this automatic…
Lockout
E012
Flame loss. When flame loss during combustion occurs twenty times consecutively despite restart attempts, the system stops supplying fuel an…
Lockout
E016
Heat exchanger overheat (bimetal). The bimetal overheat controller on the heat exchanger tripped during combustion or standby, switching the…
Details
E030
Exhaust overheat. The exhaust overheat controller shuts the unit down when the flue temperature sensor sees over 230 °F (110 °C), clearing a…
Details
E031
Burner overheat. When the burner overheat-prevention fuse opens and stays open, the boiler locks out with this manual-reset error, so check …
Details
E046
Heat exchanger thermistor / high limit switch. The control detected a fault in the heat exchanger thermistor or its high limit switch circui…
Details
E047
Exhaust thermistor. The control detected an open or shorted exhaust thermistor, so check the thermistor connection to the PCB and replace it…
Details
E060
Dual venturi error. This error appears when the Dual Venturi wiring is disconnected or the component malfunctions, locking the boiler out un…
Details
E109
Fan motor RPM error. The system checks the fan RPM signal after start-up and displays this manually cleared error when the RPM stays low or …
Details
E110
Exhaust blockage / air pressure error. The boiler senses the air volume and fan RPM and shows this error when the initial fan auto-adjust wa…
Details
E127
Abnormal APS. The air pressure sensor is abnormal (open, short, initial value or no answer) and raises this alarm, so check the sensor and i…
Details
E205
Heat exchanger outlet thermistor. The control detected an open heat exchanger outlet (supply) temperature sensor, shown as a reading of 14 °…
Details
E218
Heat exchanger inlet thermistor. The control detected an open heat exchanger inlet (return) temperature sensor and initiates boiler shutdown…
Details
E278
System supply temperature sensor. The control detected an open system supply temperature sensor and shuts the boiler down, so check the exte…
Details
E279
System return temperature sensor. The control detected an open system return temperature sensor and shuts the boiler down, so check the exte…
Details
E291
Supply/return inversion limit. The system stops operation when the return temperature rises more than 10 °F (5.5 °C) above the supply temper…
Details
E302
Low water pressure. The water pressure sensor detected pressure below the low-pressure standard (parameter 15, default 6 psi) for more than …
Details
E352
High water pressure. The water pressure sensor detected pressure above the high-pressure standard (parameter 16, default 70 psi) for more th…
Details
E353
Water pressure sensor. The control detected the water pressure sensor output outside the normal 0.5–3.5 V range for three seconds and initia…
Details
E480
DHW tank temperature sensor. The control detected an abnormal domestic hot water tank thermistor and raises this alarm, so check the tank se…
Details
E515
Abnormal PCB. An internal PCB circuit fault (resistance, transistor or relay feedback) or abnormal communication between the PCB and the gas…
Details
E517
Abnormal DIP switch setting. The DIP switch settings on the PCB are not set correctly for the model and gas type, so change the switches to …
Details
E594
Abnormal EEPROM. Communication within parts of the PCB became abnormal, so reset the unit or cycle power and replace the main PCB if the E59…
Details
E615
Abnormal PCB input / memory. The PCB received abnormal input signals, for example from the heat exchanger high limit switch or the flame rod…
Lockout
E736
Cascade communication. The boiler could not communicate with the cascade system and raises this alarm, so check the cascade wiring connectio…
Details
E740
Outdoor temperature sensor. When the outdoor sensor reads out of the normal range (under 2.2 kΩ or over 122.2 kΩ) for three seconds and the …
Details
E765
Abnormal external pump / flow switch. The contact signal of the FLOW SW terminal stayed open for thirty seconds while the boiler pump was op…
Details
E774
Manual reset limit. The external manual-reset limit device signalled a fault (its contact read short for more than five seconds with the def…
Details
E775
Auto reset limit. The external auto-reset limit device signalled a fault (its contact read short for more than five seconds with the default…
Details
E777
Low water cutoff (LWCO). The external low water cutoff device signalled an open condition for more than five seconds, so the boiler stops ig…
Lockout
E782
Main panel communication. The boiler PCB could not communicate with the front panel, so check the panel wiring, reset the unit, and replace …
Details
E784
Zone controller communication. The boiler PCB could not communicate with the zone controller, so check the zone controller wiring, reset the…
Details
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Describe what the boiler is doing and get a straight answer about the next step.
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