Navien NCB-180 Installation & Operation Manual page 19

Oxygen Elimination
This boiler may only be installed in a pressurized closed-loop
heating system, free of air (oxygen) and other impurities. To avoid
the presence of oxygen, ensure all of the air is removed from
the system during commissioning via strategically placed and
adequately sized air removal devices, located throughout the
heating system.
The Navien NCB boiler has a built-in air vent on top of
Note
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the internal circulator to efficiently remove the air in
the space heating system.
See the examples of system application at the end of
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this section detailing the installation location of the
air removal device, in case an additional air removal
device is required for a specific application.
WARNING
Immediately repair any leaks in the system plumbing to
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avoid the addition of make-up water; make-up water
provides a source of oxygen and minerals that may lead to
heat exchanger failure.
Failure to follow these instructions will result in poor
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performance, unnecessary wear of system components and
premature failure.
3.1.2 Essential Elements in a Space Heating System
Low Water Cut Off (LWCO) Device
Internal LWCO
The Navien NCB boiler is equipped with a factory-installed,
pressure-sensing type low water cutoff (LWCO) device. The
minimum operation pressure for this device is 7.3 psig.
The boiler performs water replenishment
Note
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automatically when the built-in water pressure sensor
detects insufficient water level in the boiler system.
If the water replenishment is not completed after
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5 minutes, error code E351 is displayed on the front
panel requiring a manual boiler reset.
Refer to local codes to determine if a LWCO device is required
for your system and ensure that the built-in device meets the
requirements. Install a backflow preventer in the make-up water
line to the unit if required by local codes.
18 Installing the System Piping
External LWCO
Install a separate LWCO device if required by local codes. The
following figure illustrates an example of typical LWCO installation.
External
LWCO
The external LWCO must be installed at least 6 in (150 mm) above
the top of the boiler. Refer to the following diagram for typical
wiring connections of the LWCO to the boiler PCB.
CN23 CN10
Remove the factory installed jumper on the LWCO
Note
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terminals (CN24) prior to connecting the LWCO.
The boiler supplies 24 VAC at the LWCO power
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terminals (CN25).
CN24 CN25
Common Hot