351Error; E351 Abnormal Auto Feeder Valve - Navien NCB-180 Service Manual

5.2.13 351Error

Error conditions and Check Items
Error
If the water pressure sensor senses low water level as the heating pipe pressure is low, the system stops
E351
operation of the boiler, and refills water automatically.
Abnormal Auto
If water is supplied by auto feeder valve open over 5 minutes, the error(E351) is detected and displayed on the
feeder valve
front panel. If this occurs, the boiler initiates shutdown.
1. Water is not refilled.
2. Water overflows through condensed water hose.
Check items
3. Check if water leaks from the heating pipe.
4. Check the auto feeder.
5. Check the water supplied pipe open.
6. Check the water pressure.
104 NCB Service Manual
Check if the cold water valve is closed or frozen.

Check if the auto feeder valve works normally.

Check the left drain valve of the main heat exchanger.

Check if water leaks due to a defective heat exchanger.

Leaking in unit
NO
Is the auto feeder valve
normal?
Yes
Is the DHW cold water
valve open?
Yes
1. Check DHW cold water pressure
2. Check connecter
(#1,#2 and #3 of CN 22)
3. Check the water pressure sensor
Description
Yes
Check leaking in unit
NO
Replace the auto feeder valve
NO
Open the DHW cold water valve
Version 1.0