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

5.2.18 Error 407

Error conditions and checklist
Error
E407
Hot water outlet thermistor open or short
Check items
If an error (open: -10°C or lower) in the DHW Outlet Elbow input temperature sensor is
detected, the system displays the 407E error on the front panel.
1. Check if the hot water temperature sensor connector is wet due to any reason and if
the connector is connected properly.
2. Check if the temperature sensor is open or short.
Is the DHW outlet
thermistor normal?
Yes
Check connector
Description
No
Replace the DHW outlet thermistor
Before measuring resistance of the
thermistor, detach the connector
from the PCB.
Troubleshooting 95