Considerations For System Applications - Navien NFC-175 Installation & Operation Manual

2. Close the manual and automatic air vents and the boiler drain
valve.
3. Fill the boiler to the correct system pressure. The correct
pressure will vary with each application. The typical cold water
fill pressure for a residential system is 12 psi. The pressure
will rise when the boiler is turned on and the system water
temperature increases. The operating pressure must never
exceed the relief valve pressure setting.
4. At initial fill and during boiler start-up and testing, check
the system thoroughly for leaks. Repair any leaks before
proceeding further.
WARNING
Eliminate all system leaks. The continual introduction of fresh
makeup water will reduce boiler life. Minerals can build up in
the heat exchanger, reducing heat transfer, overheating the
heat exchanger and causing heat exchanger failure.
The system may have residual substances that could affect water
chemistry. After the system has been filled and leak tested,
verify that water pH and chlorine concentrations are within the
acceptable range by performing sample testing.
CAUTION
Before operating the boiler for the first time, ensure that the
boiler system is filled with water. Purge the air inside the
system to avoid damage to the boiler.
30 Installing the System Piping

3.6 Considerations for System Applications

Read and follow the guidelines listed below when installing system
piping for the Navien NFC boiler:
System application drawings are intended to explain the system
●
piping concept only.
For the upstream side of all pumps, use straight pipes with a
●
minimum inside diameter of
Provide a system expansion tank following the guidelines on
●
page 21.
Installations must comply with all local codes. In Massachusetts,
●
a vacuum relief valve must be installed in the cold water line per
248 CMR.
Air Removal
The boiler and system piping layout must be configured to
promote the removal of air from the system. Air vents and bleeders
must be strategically placed throughout the system to aid in
purging the air from the system during commissioning of the
boiler. The system must also employ the use of an air removal
appliance, such as an air scoop or an air eliminator designed to
remove the air from the water as it flows through the system.
Follow the installation instructions included with the air removal
appliance when placing it in the system; air removal appliances
generally work better when placed higher in the system. Always
locate air removal appliances in areas of the system that have a
guaranteed positive pressure, e.g., in close proximity to the water
fill and expansion tank.
Connecting an air vent on top of the boiler is
Note
recommended.
Expansion Tank
The expansion tank must be sized in accordance with the water
volume of the system as well as the firing rate of the appliance.
It is important to locate the expansion tank, and make-up water
connection, on the inlet side of any pump in the system, as doing
so will guarantee the lowest pressure in the system will be at least
equal to the tank and make-up water pressure.
Ensure the expansion tank cannot become isolated from the
boiler anytime the system is operating. Failure to follow these
instructions may lead to discharge from the pressure relief valve,
which may result in property damage or injury.
The installation of check valves, motorized valves or
Note
other shutoff appliances (other than for the purpose of
servicing) are not permitted between the location of
the "Closely Spaced Tees" and the expansion tank.
/ in (12 mm).
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