Navien NCB300-28K Service Manual page 72

5.2.8 Error 046
5.2.9 Error 047
Error Conditions and Checklist
Is the heat exchanger's
thermistor operating
correctly?
No
Is the resistance
within the normal range?
No
Replace heat exchanger
thermistor.
Is the exhaust thermistor
operating correctly?
Yes
Check connection
Yes
Check connections
Step 1: Flush, clean Filter
Yes
Step 2: Restart
Step 3: Replace PCB
No
Replace exhaust thermistor
Troubleshooting 71