Navien NCB-180, Service Manual

Page: 115 / 149

112 NCB Service Manual Version 1.0
5.2.18 439Error
Error occurrence conditions and check items
Error Description
E439
Flow sensor error
As one or more units are operating in the cascade system, if no flow is detected during DHW using, the system
considers it as a defective flow sensor. The system displays 439E (cleared manually) on the front panel and
switches the unit operation into the Lock-Out mode (gas valve and ignition transformer locked).
Check items
1. Check the supply of cold water while the cascade system is disabled. (frozen/locked valve).
2. Defective flow sensor.
3. Defective PCB.
Disable cascade operation and
open faucet
Check cold water supply
Check flow sensor connector (CN5)
Clean water flow sensor
Is there water flow?
NO
Yes