Navien NCB-180 Service Manual page 116

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Fault Possible Causes
Cold water supply
No hot water flow
Boiler not
Defective flow sensor
working
Other trouble Defective PCB
Emergency measures for a defective flow sensor
Replacement of the part is usually required for the boiler to operate when an error occurs with the flow sensor. If it is impossible to
replace the part immediately, use the following emergency measures.
If the flow sensor impeller is stuck due to foreign substances:
Remove the flow sensor and blow air through the part from the inlet side. If the impeller does not rotate, disassemble the impeller, and
remove the foreign substance before reassembling it.
If the flow displayed on the front panel is 0.0, and the impeller rotates when you blow into it, the flow sensor will need to be replaced.
1. Drain water from the unit, then remove the flow sensor (refer to page 127).
2. Blow air through the flow sensor. Check that the impeller rotates freely.
1. Check if the cold water line is frozen.
error
2. Check if the cold water filter is clogged.
1. Check the current flow displayed on the front panel.
If the flow sensor is defective, the displayed flow value is 0.0 while water

flows from the hot water tap.
Remove the flow sensor and blow into it. The rotation detector on the flow

sensor is defective if the impeller rotates and display remains 0.0.
* Component Test mode may also be used to check the operation of the flow sensor
(refer to page 21).
2. Check connector assembly and contact of the flow sensor.
3. Check the input voltage of the flow sensor.
Operating voltage (Black + Red) : Defective PCB if DC 12 V is not supplied.

4. Replace the flow sensor if no flow is detected while the operating voltage is
normal.
If the issue continues despite the checking of items above the PCB is defective.
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