Navien NFC-175, Service Manual

Page: 82 / 138

82 NFC 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 if a gas valve is opened or not.
2. 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.
3. 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.
4. Check the static pressure at stand by.
Check the dynamic pressure at MAX combustion (2nd stage MAX combustion
setting: DIP S / W 1-1 ON).
5. Check the gas pipe connector.
●
If a CSST connector has been used, check to ensure that it is not been over
tightened resulting in the seal obstructing gas flow.
6. 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 BTU/h
7. If too much pressure is exerted on the nut component while installing the gas
pipe may reduce the gas supply due to packing push-out and Teflon blockage,
etc.
Flame loss and noise
occurs after ignition
PCB DIP switch setting
error
Check the PCB DIP switch settings (refer to page 20).
1 2 3 4 5 6
O
N
O
N
O
N
O
N
1 2 3 4 5 6 7 8
1
NG LP
1
Offset pressure
adjustment error
Low fire (1-stage Min) offset adjustment error
●
Use the Front Panel to set the unit at “1st MIN” (refer to page 48).
●
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.