Navien NCB300-28K, Service Manual

Page: 91 / 108

90 Replacement of Parts
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 clip on the back of the flow sensor.
Figure 16
5. Remove the flow control valve and the flow sensor by
turning the valve left.
6. Replace it with the new flow control valve and sensor.
7. Turn on water supply, power supply, and gas supply to the
unit.
8. Carefully open a hot water tap and ensure there are no leaks
at the flow sensor connections.
6.2.8 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. Loosen the central heating return pipe adapter.
Figure 14
5. Remove the four screws and clip at the bottom of the cover.
Figure 15
6. Reinstall the pump drain plug at the bottom of the unit.
7. Reconnect the wiring connector at the pump.
8. Install the Front panel back onto the unit by using the four
screws.
9. Turn on water supply, power supply, and gas supply to the
unit.
10. Open a hot water tap and ensure that there are no leaks at
the pump connections.
11. Open the air vent on top of pump to release air within the
system.