Navien NCB300-28K, Service Manual

Page: 56 / 108

Troubleshooting 55
Error Code Sub Code Function Diagnosis/Actions
E205
1
Heating supply thermistor open
error
1. Check the thermistor.
2. Check pump wiring connections.
2
Heating supply thermistor short
error
E302 0 Low water pressure
1. Check filling loop and pressurise system to 1.0 - 1.3 bar.
2. Check the incoming water pressure and activity at the PRV.
E407
1
Hot water outlet thermistor open
error
1. Check the thermistor.
2. Replace the thermistor.
2
Hot water outlet thermistor short
error
E515
Abnormal operation: Relay
feedback (PCB)
E517 0
Abnormal operation: DIP switch
setting (PCB)
Check the dip switches on the front panel and the PCB.
E594 0
Abnormal operation: EEPROM
(PCB)
Check the PCB.
E615
Abnormal operation: Input and
memory (MCU)
E740 1
Abnormal operation: Outdoor
temperature sensor
1. Ensure that outdoor reset curve is correctly configured.
2. Check the outdoor temperature sensor’s wiring connections.
E782 0
Abnormal operation: Main panel
communication
Check the PCB.
E783 0
Abnormal operation: OpenTherm
remote control
E787 1 Abnormal operation: Reset device
E788 0
Abnormal operation: Gas type
settings
If the actions contained in the table above do not resolve the boiler fault, contact the
Navien technical support team on 1-800-519-8794
.
To assist with fault resolution, error codes are displayed on the front panel and saved on a PCB board in the boiler providing a record of
the faults and failures that occur.
IMPORTANT
To reset the boiler, either press [Reset] on the front panel or turn off the boiler’s power supply and then turn it on again.