Navien NCB-700-2S+/42K Service Manual page 64

Error Code Sub Code
E109 0 Fan motor activity error
Exhaust blockage (Condensate
E110 0
blockage)
E127 0 APS error
Heating supply thermistor open
1
error
E205
Heating supply thermistor short
2
error
Heating return thermistor open
1
error
E218
Heating return thermistor short
2
error
E291 3 Supply / Return inversion limit
E302 0 Low water pressure
E352 0 High water pressure
1 Water pressure sensor open error
E353
2 Water pressure sensor short error
Hot water outlet thermistor open
1
error
E407
Hot water outlet thermistor short
2
error
Cold water inlet thermistor open
1
error
E421
Cold water inlet thermistor short
2
error
Abnormal operation: Flow control
E434 1
value
DHW Outlet 2 thermistor open or
E441 1
short circuit
E445 1 Abnormal operation: Mixing valve
1 DHW tank thermistor open circuit
E480
2 DHW tank thermistor short circuit
Abnormal operation: Relay
E515
feedback (PCB)
Function
1. Check and clean the air intake filter.
2. Check and clean the fan motor.
3. Test the voltage from the PCB to ensure that it is correct. Replace
1. Check the exhaust pipe for obstructions.
2. Check and clean the intake air filter.
3. If possible, remove the exhaust pipe to ensure that the flue is clear.
1. Check the APS.
2. Check APS wiring connections
1. Check the thermistor.
2. Check pump wiring connections.
1. Check the thermistor.
Check the direct water connection.
1. Check the feeder valve.
2. Check the incoming water pressure and activity at the PRV.
1. Check the feeder valve.
2. Check the incoming water pressure and activity at the PRV.
Check the water pressure sensor.
1. Check the thermistor.
2. Replace the thermistor.
1. Check the thermistor.
2. Replace the thermistor.
Diagnosis/Actions
fan if PCB voltage is normal.
Troubleshooting 63