439Error - Navien NCB-180 Service Manual

5.2.18 439Error

Error occurrence conditions and check items
Error
As one or more units are operating in the cascade system, if no flow is detected during DHW using, the system
E439
considers it as a defective flow sensor. The system displays 439E (cleared manually) on the front panel and
Flow sensor error
switches the unit operation into the Lock-Out mode (gas valve and ignition transformer locked).
1. Check the supply of cold water while the cascade system is disabled. (frozen/locked valve).
Check items
2. Defective flow sensor.
3. Defective PCB.
112 NCB Service Manual
Disable cascade operation and
open faucet
Is there water flow?
Yes
Check flow sensor connector (CN5)
Clean water flow sensor
Description
NO
Check cold water supply
Version 1.0