777Error - Navien NHB-055 Service Manual

5.2.26 777Error

Error conditions and Check Items
Check the
connecting
terminals
(CN25)
Check method
Fault
E777
Version 1.0
Is the LWCO 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
2. Check the output voltage normal.
installed jumper
No
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
NHB Service Manual 121