Navien NPE-240A Service Manual

Troubleshooting 107
5.1.16 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 while the system opens the
water adjustment valve, 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.
Check flow sensor connector (CON6)
Clean water flow sensor
Disable cascade operation and
open faucet
Check cold water supply
NO
Is there water flow?
Yes

Navien NPE-240A Specifications

General

Type	Tankless
Fuel Type	Natural Gas or Propane
Energy Factor	0.97
Energy Efficiency	97%
Voltage	120V
Ignition Type	Electronic
Maximum Input	199, 900 BTU/h
Water Connection Size	3/4"
Gas Connection Size	3/4"
Warranty	15-year on heat exchangers, 5-year on parts, 1-year on labor
Dimensions	17.3" W x 13.2" D x 27.4" H