Navien NCB-180, Service Manual

Page: 130 / 149

6.2.9 Flow Sensor
1. Turn off the gas supply to the unit.
2. Disconnect the unit from the power supply.
3. Turn off the water supply to the unit. Drain all water
from the appliance.
4. Remove the main gas valve (refer to page 125)
5. Remove the stainless fastener.
Figure 18
6. Remove two screws of Domestic Cold Water Inlet
Adaptor from bottom of case.
Figure 19
7. Detach the 2 wire connectors that connect the flow
sensor to the PCB.
8. Pull out the flow sensor.
Figure 20
9. Replace with old flow sensor with the new part.
10. Reinstall the flow sensor into heat exchange and
reattach the stainless clip. Ensure that the flow sensor is
properly connected to the heat exchanger and that the
clip is tightly holding the two parts together.
11. Reinstall the two screws at the flow sensor to secure the
part to the Domestic Cold Water Inlet Adaptor.
12. Turn on water supply, power supply, and gas supply to
the unit.
13. Carefully open a hot water tap and ensure there are no
leaks at the flow sensor connections.
6.2.10 Circulation Pump
1. Turn off the gas supply to the unit.
2. Disconnect the unit from the power supply.
3. Turn off the water supply to the unit.
4. Open the drain plug on the pump and Remove the 4
screws from the bottom of the case.
Figure 21