| E773 | Improper Gas Type Detected | Critical |
| E001 | Ignition Failure | Warning |
| E003 | Abnormal Ignition | Warning |
| E004 | False Flame Detection | Warning |
| E012 | Flame Loss | Warning |
| E016 | Overheating | Warning |
| E030 | Exhaust Overheat Sensor | Warning |
| E031 | Inlet Thermistor Open/Short | Warning |
| E046 | Outlet Thermistor Open/Short | Warning |
| E047 | DHW Thermistor Open/Short | Warning |
| E060 | Fan Motor Abnormality | Warning |
| E109 | Fan Motor Speed Low | Warning |
| E110 | Exhaust Blocked | Warning |
| E205 | Water Flow Sensor Failure | Warning |
| E218 | Bypass Servo Motor Failure | Warning |
| E238 | Abnormal recirculation pump operation ● The pump is turned ON. ● Water flow is N | Warning |
| E278 | Mixing Valve Stuck | Warning |
| E279 | Mixing Valve Open Failure | Warning |
| E291 | Cascade Communication Error | Warning |
| E302 | Remote Controller Communication | Warning |
| E311 | Abnormal water level | Warning |
| E351 | Abnormal Auto Feeder Valve | Warning |
| E352 | APS Sensor Abnormality | Warning |
| E353 | APS Sensor Open/Short | Warning |
| E360 | Abnormal cover opening | Warning |
| E407 | Dom.Hot Water Outlet Sensor | Warning |
| E421 | Dom.Cold Water Inlet Sensor | Warning |
| E434 | Abnormal Water Adjust Valve | Warning |
| E438 | Navien Error Code E438 - Abnormal Operation | Warning |
| E439 | No Dom.Water Flow Detected | Warning |
| E441 | Dom.Hot Water Outlet2 Sensor | Warning |
| E445 | Abnormal Mixing Valve | Warning |
| E480 | BMS Communication Error | Warning |
| E515 | Low Water Flow | Warning |
| E517 | Water Flow Switch Failure | Warning |
| E593 | Abnormal Panel Key | Warning |
| E594 | Condensate Blockage | Warning |
| E615 | PCB Communication Failure | Warning |
| E736 | CH Return Thermistor Failure | Warning |
| E740 | CH Buffer Tank Thermistor | Warning |
| E761 | Pump Aquastat Not Detected | Warning |
| E762 | Dual Venturi Failure | Warning |
| E774 | Abnormal external safety system operation 1 | Warning |
| E775 | Abnormal external safety system operation 2 | Warning |
| E777 | System Error Code | Warning |
| E782 | Internal PCB Fault | Warning |
| E784 | Outdoor Temp Sensor Failure | Warning |
| E786 | Header Thermistor Failure | Warning |
| E788 | Pump Failure | Warning |
| E799 | Leak detected (sensor) | Warning |
| E805 | Abnormal supply air- temp sensor operation for lower limit | Warning |
| E810 | Abnormal circulator operation (inoperable) | Warning |
| E811 | Abnormal circulator operation (inoperable) | Warning |
| E818 | Abnormal return air- temp sensor operation for lower limit | Warning |
| E822 | Overcooling of the air conditioning coil (Evaporator coil). | Warning |
| E860 | Replace the circulator filter with a new one, and then reset the furnace. | Warning |
| E890 | Abnormal circulator communication | Warning |