777Error - Navien NCB-150E Service Manual

5.2.25 777Error

Error conditions and Check Items
Check the
connecting
terminals
(CN25)
Check method
Fault
E777
Is the LWCO
No
installed properly?
Yes
Is proper power being
supplied to the LWCO?
Yes
Check LWCO
Possible Causes
1. Check the factory installed jumper and jumper connection.
Abnormal factory
installed jumper 2. Check the output voltage normal.
Is the factory jumper
installed properly
on CN24?
Yes
Is the output
voltage normal on
CN25? (AC 24V)
No
Replace the main PCB
Check method
Check the output voltage ( Normal voltage : AC 24V)
Check the factory
No
installed jumper
and jumper
connection (CN24)
Yes
Troubleshooting 129