Navien NFC-175, Service Manual

Page: 95 / 138

NFC Service Manual 95 Version 1.0
5.2.12 205Error
Error conditions and Check Items
Error Description
E205
Heat exchanger output temperature
sensor open
If an error (open: 14°F (-10°C) or lower) in the heat exchanger input temperature sensor is
detected, the system displays the 205E error on the front panel. If this occurs, the boiler initiates
shutdown.
Check items
1. Check if the heat exchanger output temperature sensor connector is wet due to any
reason, including leakage.
2. Replace the defected heat exchanger output temperature sensor.
3. Check circulation pump (external type) operating status and for proper flow through the
space heating line.
4. Check the voltage on the PCB to verify proper power to the pump. If there is no voltage,
replace PCB. Otherwise, bleed out air from the system before resetting the unit. If issue
persists, replace the pump.
Is the outlet thermistor
normal?
Check connector
(#7 and #8 of CNJ1)
Replace outlet thermistor
Resistance between #7 and #8 of CNJ1
is from 0.437kΩ to 176kΩ at normal
condition. (see page 50 for Wiring
Diagram)
No
Yes
Before measuring resistance of the
thermistor, detach the connector
from the PCB.