Navien NCB-180, Service Manual

Page: 91 / 149

88 NCB Service Manual Version 1.0
Check method
Fault Possible Causes Check method
Flame loss and
noise occurs after
ignition
Low gas supply
pressure
1. Check the gas supply pressure.

NG: 3.5” - 10.5” W.C, LP: 8” - 13.5” W.C

LP pressure drop occurs frequently in the winter.
2. While the static pressure is normal, the use of another gas appliance may cause a
possible drop in gas pressure to the unit. Therefore, it is required to check the
dynamic pressure.
Check the static pressure: Gas supply pressure during stand by.
Check the dynamic pressure: Gas supply pressure at (2nd stage MAX combustion setting:
DIP S/W 1-1 ON) MAX combustion
3. Check the gas pipe connector.

If a CSST connector has been used, check to ensure that it is not been
overtightened resulting in the seal obstructing gas flow.
4. Check the gas meter capacity (Example)

Gas meter Boiler Furnace Domestic gas stove
425 CFH (Gas Meter) ≥
195 CFH ( 58.8 CFH (Furnace)
+ 63.7 CFH (Domestic gas stove)
CFH = 1,020 Btuh
Flame loss and
noise occurs after
ignition
PCB DIP switch
setting error
Check the PCB DIP switch settings.(Refer to page 21)
Offset pressure
adjustment error
Low fire (1-stage Min) offset adjustment error

Use the Front Panel to set the unit at "MIN.1" (refer to page 54).

Open the offset pressure port on the gas valve and connect a manometer.
Use the positive pressure side on a dual port manometer.

Adjust the offset pressure by turning the adjustment screw on the gas valve
with a 5/32" or 4mm Allen wrench, if the pressure value is out of range.