Flow Sensor - Navien NCB300-28K Service Manual

4.7.9 Flow Sensor

Item Description
Function To detect water flow in LPM (litres per minute) to provide a steady hot water temperature.
1. Unable to detect or measure water flow rate.
Fault
2. Damage to and/or leakage from the water flow sensor.
1. Ignition does not start.
Symptoms
2. Boiler operation stops when water leakage is detected.
Error codes E439
1. Visual inspection: Check wire connections are secure and inspect for wire damage.
Diagnostics
2. Visual Inspection: Check for sensor damage and for scale forming on the sensor.
System Details 45