031Error - Navien NFC-175 Service Manual

5.2.35 777 & 031Error
No. Error code
777
LWCO
8 (Decompression
transformer
error)
Version 1.0
Cause
1. If a LWCO sensor is not equipped,
(1) Check the controller connection terminal.
(2) Check the decompression transformer harness.
(3) Change the decompression transformer.
(4) Change the PCB.
2. If a LWCO sensor is equipped,
(1) Check pipe leakage.
(2) Check if the LWCO sensor harness is disconnected.
(3) Change the LWCO sensor.
When LWCO signal
is detected to Open
more than five
(4) Change the decompression transformer.
seconds, the system
determines that
there is no water
(5) Change the PCB.
in the boiler and
piping, stops the
ignition and pump,
and outputs a LWCO
Decompression transformer
error message.
Check the connection
of the decompression
transformer harness.
When a LWCO sensor is not equipped, there is a terminal connecting the two holes
in the controller. An error can occur if the terminal is not connected completely.
If the problem persists after completing (1), check if the settlement of the
controller connector is right or it is disconnected.
If the problem persists after completing (1) and (2), change the decompression
transformer.
If the problem persists after completing all the actions above, change the PCB.
If decompression failed, an error occurs. Check if there is a leakage in the heating
line.
If the problem persists after completing (1), check if the LWCO sensor harness is
disconnected.
If the problem persists after completing (1) and (2), change the LWCO sensor.
If the problem persists after completing (1), (2), and (3), change the decompression
transformer.
If the problem persists after completing all the actions above, change the PCB.
Check method
Check the terminal
connection status
NFC Service Manual 117