205Error - Navien NCB-150E Service Manual

5.2.12 205Error

Error conditions and Check Items
Error
E205
Heat exchanger output temperature
sensor open
Check items
112 NCB-E Service Manual
If an error (open: 14°F (-10°C) or lower) in the heat exchanger input temperature sensor is
detected, the system displays the 421E error on the front panel. If this occurs, the boiler initiates
shutdown.
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 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,
bleed out air from the system before resetting the unit. If issue persists, replace the pump.
Is the inlet thermistor
normal?
Yes
Check connector
(#7 and #8 of CN 13)
Description
NO
Replace outlet thermistor
Resistance between #7 and #8 of CN13
is from 0.437kΩ to 176kΩ at normal
condition.
(see page 60 for Wiring Diagram)
Before measuring resistance of the
thermistor, detach the connector
from the PCB.
Version 1.4