Navien NCB-180 Service Manual page 85

Check method
Failure mode
Gas supply error
Ignition failure
Check gas supply pressure(Refer to page 23)
Defective electrode gap
and shape
82 NCB Service Manual
Cause
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

425 CFH (Gas Meter) ≥ 195 CFH (Boiler)+ 58.8 CFH (Furnace)

CFH = 1,020 Btuh
Digital pressure
manometer
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.
Check method
Boiler Furnace Domestic gas stove
+ 63.7 CFH (Domestic gas stove)
A shifted seal narrows the inner diameter of
CSST connector
Version 1.0