Navien NCB300-28K, Service Manual

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50 System Details
4.7.14 3 Way Valve
Item Description
Function
Uses a DHW flow sensor and PCB to cycle water between the space heating system and the DHW heat
exchanger.
Fault
1. No hot water in space heating mode.
2. No domestic hot water in DHW mode.
Symptoms
DHW supply stops and flow continues in the space heating system when the space heating water
temperature is lower than the set point.
Error codes E016
Diagnostics
1. Visual inspection: Check the 3-way valve wiring connections.
2. Voltage test: Test the voltage meets the specifications shown below.
Testing/inspection
information
●
SPACE HEATING: RED + WHITE: ON AC 230 V, OFF 0 V
●
DHW: RED + PURPLE: ON AC 230 V, OFF 0 V

Confirm voltage as the 3-way valve operating