Navien NCB-700-2S+/42K Service Manual page 70

Testing method
Error type
Gas supply fault
Ignition failure
Electrode gap and shape
Cause
1. Check if the main gas valve is open.
2. Check the gas supply pressure.
NG: 17-25 mbar, LP: 25-35 mbar
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LP pressure drops can occur during winter.
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3. Check the diameter of the flexible pipe to ensure it is compatible with the boiler.
4. If a CSST connector is used, ensure that it has not been overtightened. An
overtight connection can deform the seal and obstruct the flow of gas.
5. Check the class of pressure meter.
Digital pressure
manometer
Check gas supply pressure
Insufficient electrode gap and deformed electrodes can prevent ignition.
Recommended gap: approx. 3-4 mm (1/8"). Replace electrode if defective.
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Ignition can fail due to improper gap even if the discharge appears normal in the
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faults
flame monitoring window. Disassemble to gain access to the electrode and inspect
the gap.
Testing method
Deformed seal can obstruct the internal
diameter of CSST connectors
Troubleshooting 69