Navien NCB-180, Service Manual

Page: 85 / 149

82 NCB Service Manual Version 1.0
Check method
Failure mode Cause Check method
Ignition failure
Gas supply error
1. Check if the main gas valve is open.
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. Check the flexible pipe diameter for compatibility with the boiler.
4. 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.

Static pressure: Gas pressure during stand by.

Dynamic pressure: Gas pressure at max combustion. (2nd stage MAX
combustion setting: DIP S/W 1-1 ON)
5. If a CSST connector has been used, check to ensure that it is not been
overtightened resulting in the seal obstructing gas flow.
6. Check the meter class (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
Defective electrode gap
and shape
Defective electrode gap and shape disables ignition.

Appropriate electrode gap: approx. 3~4mm(1/8") (replace if defective)

An ignition fail may occur due to improper gap, while discharge seems
normal when checked via the flame monitoring window. Therefore, it is
required to check the gap after disassembly.
Digital pressure
manometer
Check gas supply pressure(Refer to page 23)
A shifted seal narrows the inner diameter of
CSST connector