Navien NHB-055, Service Manual

Page: 87 / 147

NHB Service Manual 87 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.
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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.
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.
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Static pressure: Check the gas pressure at stand by mode.
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Dynamic pressure: Check the 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 over tightened
resulting in the seal obstructing gas flow.
6. Check the meter class (Example)
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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
Digital pressure
manometer
Check gas supply pressure (Refer to page 17) A shifted seal narrows the inner diameter of
CSST connector
Defective electrode gap
and shape
Defective electrode gap and shape disables ignition.
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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.