Navien NCB-150E Service Manual page 92

Check method
Failure mode
Gas supply error
Ignition failure
Check gas supply pressure(Refer to page 23)
Defective electrode
gap and shape
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
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LP pressure drop occurs frequently in the winter.
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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.
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Dynamic pressure: Gas pressure at max combustion. (2nd stage MAX combustion
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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
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425 CFH (Gas Meter) ≥ 195 CFH (Boiler)+ 58.8 CFH (Furnace)
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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)
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An ignition fail may occur due to improper gap, while discharge seems normal when
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checked via the flame monitoring window. Therefore, it is required to check the gap
after disassembly.
Check method
Furnace Domestic gas stove
+ 63.7 CFH (Domestic gas stove)
A shifted seal narrows the inner diameter of CSST
connector
Troubleshooting 91