Navien NCB-180 Service Manual page 87

Failure
Cause
mode
Main gas valve
Ignition
failure
84 NCB Service Manual
1. Check the primary/secondary power supply to the main gas valve.
Check, with a multi-meter, if the input power is DC 22-24 V.
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2. Replace the PCB if power is not supplied.
3. If power supply is normal, check if the coil is open.
Check the resistance. (refer to page 125)
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4. Check if the solenoid valve works properly.
Feel or hear a click.

PIN No.
Check if the coil is open (Proper resistance range : 100~1,000 Ω)
Check the voltage of the solenoid valve / White-Yellow, White-Red
Check method
Version 1.0