Navien NCB300-28K, Service Manual

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62 Troubleshooting
Error type Cause Testing method
Ignition failure
Main gas valve
1. Test the primary and secondary voltages at the main gas valve.
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Use a multimeter, between the YELLOW - WHITE wires and verify the voltage is
DC 24 V
2. If there is no voltage, replace the PCB.
3. If the voltage is correct, check if the coil is open.
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Check the resistance. Check if the solenoid valve works correctly.
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Feel or listen for a click.
Check that the coil is open (Correct resistance range: 100-1,000Ω)
Check the voltage at the solenoid valve / Yellow - White