Navien NFC-175, Service Manual

Page: 73 / 138

NFC Service Manual 73 Version 1.0
Check method
Failure mode Cause Check method
Abnormal circulation
Defective circulation
pump(external)
If the unit is in error condition, the circulation pump and fan run continuously.
In the event the unit is not in error condition, enter Test mode for the connection
(see page 43, Diagnosing the Boiler System).
The heating strainer is
clogged
1. Check if the strainer is clogged with debris.
2. Check the cause of debris if the strainer is clogged (Aluminium distributor
oxidized steel, etc.)
The main heat exchanger
is clogged.
Separate the inlet / outlet pipe from the main heat exchanger, and blow air
through the heat exchanger to check if the pipe is clogged.
Valve closed
Check heating inlet / outlet valve and heating manifold piping.
At least one valve on the heating manifold must always be open.
Other potential issues
Capacity setting
Sudden increase of temperature due to PCB DIP S / W model setting error or max
setting.
Capacity
DIP S / W No.
1-5 1-6
175,000 BTU (NFC-175) ON OFF
199,000 BTU (NFC-200) OFF OFF
Defective PCB If the trouble continues despite the checking of above items, replace the PCB.