Navien NFC-175 Installation & Operation Manual page 21

Also, an external LWCO and a pressure relief valve can be installed
at the air vent connection. Refer to "Low Water Cut Off (LWCO)
Appliance" on page 21 and "Pressure Relief Valve" on page 21.
Before installing the vent line and any vent fittings,
Note
you must be familiar with the LWCO and pressure relief
valve installation guidelines.
Low Water Cut Off (LWCO) Appliance
Internal LWCO
The Navien NFC boiler is equipped with a factory-installed,
pressure-sensing type low water cutoff (LWCO) appliance. The
minimum operation pressure for this appliance is 6 psi by default.
When the built-in water pressure sensor detects
Note
insufficient water level in the boiler, error code E302 is
displayed on the front panel requiring a manual boiler
reset.
Refer to local codes to determine if a LWCO appliance is required
for your system and ensure that the built-in appliance meets the
requirements.
External LWCO
If local codes require a separate LWCO appliance, install one
separately. A LWCO may be connected to the included PRV-Air
vent Adapter. The following illustration shows an example of a
separately installed external LWCO.
The external LWCO must be installed at least 6 in (152 mm) above
the top of the heat exchanger. Refer to "3.7.2 Wiring Diagram -
External LWCO" on page 38 for typical wiring connections of the
LWCO to the boiler PCB.
External LWCO
Backflow Preventer
Install a backflow preventer valve in the make-up water supply to
the unit as required by local codes.
Expansion Tank
An expansion tank must be installed in the space heating piping
to prevent excessive pressure from building in the system. See the
examples of system application at the end of this section for the
installation location. Refer to the expansion tank manufacturer's
instructions for additional details.
Follow the guidelines below when installing an expansion tank.
Connect an air separator to the expansion tank only if the air
●
separator is located on the suction side of the system pump.
Install the make-up water connection at the same location as
●
the expansion tank's connection to the system.
When replacing an expansion tank, consult the expansion tank
●
manufacturer's literature for proper sizing.
For diaphragm expansion tanks, always install an automatic air
●
vent on the top side of the air separator to remove residual air
from the system.
Isolation Valves and Unions
Full port ball valves are required for the boiler system. Failure
●
to use full port ball valves could result in a restricted flow rate
through the boiler.
Check valves are recommended for installation. Failure to install
●
check valves could result in a reverse flow condition during
pump(s) off cycle.
Unions are recommended for unit serviceability.
●
Magnetic Filtration
The Navien NFC boiler comes with the NavicClean hydronic
heating filter. This must be connected to the space heating return
in the near boiler piping to protect the boiler from iron oxide
(magnetite). Refer to the included instructions for installation
details.
Pressure Relief Valve
To complete the space heating system installation, you must install
a / in, 30 to 80 psi (max) pressure relief valve on the space heating
3
4
hot water outlet. An ASME approved HV pressure relief valve for
space heating system is supplied with the boiler.
Installing the System Piping 21