Error - Navien NCB300-28K Service Manual

5.2.18 Error 740

Error conditions and Check Items
Error
E740
Abnormal outdoor sensor
Check items
5.2.19 Error 782
Error occurrence conditions and check items
Is the wiring from the front panel
properly connected to the PCB?
If an error (under 2.2kΩ or over 122.2kΩ) in the outdoor sensor is detected continuously
for 3 seconds, The system displays the error message E740 on the front panel. If this
occurs, the boiler changes the control mode from Reset Curve Mode to Normal Mode.
1. Check the parameter setting.
2. Check the outdoor sensor.
Is the Outdoor sensor
installed properly?
Yes
Is the outdoor thermistor
normal?
Yes
Check connecter
NO
Reconnect panel to the PCB
Description
No
Change the Outdoor Reset Control
mode setting.
No
Replace the outdoor thermistor.
Step 1: Reset the unit.
Yes
Step 2: If problem persists, replace
the PCB and front panel.
Troubleshooting 81