Navien NCB500-2S/37K Service Manual page 64

Scenario2
No No
Is the gas valve operating Is the main
Check the connections
correctly? gas valve voltage correct?
Test the voltage between WHITE-YELLOW at
Yes
CONZ1: DC 24 V
Yes
No
Check that the gas valve is
Is the gas valve open?
open or check the LP supply
For LP gas models, low gas pressure can cause
Yes
"Ignition Failure" errors.
Check the flame rod Turn OFF the boiler
Troubleshooting 63