Navien NHB-055 Service Manual page 82

Error Code Sub Code
E777 0
E782 0
E784 0
If any of the above solutions do not resolve the problem with the Boiler, contact Navien's Technical department at 1-800-519-8794.
There will be error codes displayed on the front panel and recorded on the PCB board (within the unit) of any problems or failures that occur
with the Boiler.
IMPORTANT
To reset the Boiler, either press the [Reset] button on the front panel or disconnect, then reconnect electrical power to the boiler.
82 NHB Service Manual
Function
Abnormal operation: LWCO(external device)
Abnormal Main-Panel communication
Abnormal operation: zone controller
communication (external device)
Self-diagnostic / Action
1. Check the LWCO wiring connection
2. Ensure that the system water level is appropriate.
3. Add make-up water to the system if necessary.
4. Check for proper voltage from connector
(24VAC).
Check the PCB.
1. Check the zone controller wiring connection.
2. Check the zone controller PCB
3. Check the Main and Panel PCB
Version 1.0