439Error - Navien NPE-180A Service Manual

5.1.16 439Error

Error occurrence conditions and check items
Error
As one or more units are operating in the cascade system, if no flow is detected while the system opens the
E439 water adjustment valve, the system considers it as a defective flow sensor. The system displays 439E (cleared
Flow sensor error manually) on the front panel and 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.
Disable cascade operation and
Check flow sensor connector (CON6)
open faucet
Is there water flow?
Yes
Clean water flow sensor
Description
NO
Check cold water supply
Troubleshooting 107