Navien is a South Korean heating technology company founded in 1978. Known for innovative condensing combi boilers with stainless steel heat exchangers, their NCB series is increasingly popular in the UK. Navien fault codes use three-digit numbers.
Navien Boiler Fault Codes
All Navien Fault Codes 43
| Code | Fault | Severity | Type | View guide |
|---|---|---|---|---|
| 001 | Ignition Failure The boiler has failed to ignite after multiple attempts. The gas supply, spark electrodes, or… | High | Engineer | View Guide |
| 002 | Flame Loss During Operation The flame was established but has been lost unexpectedly. This may indicate a gas supply… | High | Engineer | View Guide |
| 003 | Ignition Failure The boiler has failed to ignite — manual reset required. The most common Navien fault… | Medium | DIY Check | View Guide |
| 004 | False Flame (Auto-Reset) The boiler has detected a flame signal when not expected. This version auto-resets but if… | Medium | DIY Check | View Guide |
| 005 | Abnormal Ignition Ignition occurring outside expected parameters. | High | Engineer | View Guide |
| 006 | False Flame Signal Flame detected when gas valve should be closed. | High | Engineer | View Guide |
| 007 | Fan Fault Fan not operating within expected speed range. | High | Engineer | View Guide |
| 008 | Exhaust Blockage The flue is blocked or partially obstructed. | High | Engineer | View Guide |
| 009 | Air Pressure Switch Fault APS not detecting correct airflow. | High | Engineer | View Guide |
| 010 | Abnormal Exhaust Temperature The exhaust gas temperature is outside the normal range. The boiler has shut down as… | High | Engineer | View Guide |
| 011 | Abnormal Air Pressure The air pressure switch is not detecting correct air flow through the combustion chamber. | High | Engineer | View Guide |
| 012 | Flame Loss During Operation The boiler ignited but then lost its flame during operation. Reset required. | Medium | DIY Check | View Guide |
| 013 | Low Water Pressure System pressure below minimum. | Low | DIY Check | View Guide |
| 014 | Pump Fault Pump not running or seized. | High | Engineer | View Guide |
| 015 | PCB Fault The main printed circuit board has an internal error or communication fault. | High | Engineer | View Guide |
| 016 | Heat Exchanger Overheated The primary heat exchanger has detected an overtemperature condition. Manual reset required. | High | Engineer | View Guide |
| 017 | PCB Fault Internal PCB communication error. | High | Engineer | View Guide |
| 018 | Overheat Protection Safety thermostat activated. | High | Engineer | View Guide |
| 019 | Condensate Blocked Condensate drain blocked or frozen. | Medium | DIY Check | View Guide |
| 020 | DHW Overheat Hot water temperature exceeded safe limit. | High | Engineer | View Guide |
| 027 | Low Water Flow The water flow rate through the boiler is too low for safe operation. | Medium | Engineer | View Guide |
| 028 | Diverter Valve Fault Valve stuck or not switching. | Medium | Engineer | View Guide |
| 030 | Abnormal Exhaust Temperature The exhaust (flue gas) temperature is abnormal — either too high or there is a… | High | Engineer | View Guide |
| 031 | Flow Sensor Short Circuit Flow NTC wiring has a short. | Medium | Engineer | View Guide |
| 032 | DHW Thermistor Fault The domestic hot water temperature sensor has developed a fault. | Medium | Engineer | View Guide |
| 033 | Gas Valve Fault Gas valve not responding. | High | Engineer | View Guide |
| 034 | Return Sensor Fault Return NTC has a fault. | Medium | Engineer | View Guide |
| 035 | Flow Sensor Open Circuit Flow NTC circuit broken. | Medium | Engineer | View Guide |
| 036 | Heating Thermistor Fault The central heating temperature sensor has developed a fault. | Medium | Engineer | View Guide |
| 038 | Combustion Fault Air/gas mixture outside limits. | High | Engineer | View Guide |
| 040 | eBUS Fault Communication fault. | Medium | Engineer | View Guide |
| 041 | Frost Protection Active Frost protection running. | Medium | DIY Check | View Guide |
| 042 | Pressure Sensor Fault Electronic sensor faulty. | Medium | Engineer | View Guide |
| 046 | Heat Exchanger Overheating (Auto-Reset) Abnormal heat exchanger overheating — the boiler should auto-reset. If recurring, investigate circulation. | Medium | Engineer | View Guide |
| 109 | Fan Error The boiler fan is not operating correctly. The boiler needs resetting after checking the fan. | High | Engineer | View Guide |
| 110 | Exhaust Blockage / Condensate Blockage The exhaust system or condensate drain is blocked. On Navien boilers this is the specific… | Medium | DIY Check | View Guide |
| 127 | Air Pressure Switch (APS) Issue The air pressure switch is not operating correctly — it is not confirming adequate airflow… | High | Engineer | View Guide |
| 205 | Heating Supply Thermistor Fault The heating supply (flow) thermistor has an open or short circuit fault. The boiler may… | Medium | Engineer | View Guide |
| 218 | Heating Return Thermistor Fault The heating return thermistor has an open or short circuit fault. | Medium | Engineer | View Guide |
| 302 | Low Water Pressure The system water pressure has dropped below the safe minimum. The boiler should auto-reset once… | Low | DIY Check | View Guide |
| 352 | High Water Pressure The system water pressure is too high. The boiler should auto-reset once pressure drops. | Medium | Engineer | View Guide |
| 407 | Room Controller Communication Error The boiler has lost communication with the room controller or thermostat. | Low | DIY Check | View Guide |
| 594 | EEPROM Error (PCB) There is a memory fault on the main PCB. Contact an engineer — this cannot… | High | Engineer | View Guide |