Navien NFB-175 Mode D'emploi page 31

3.5.3 System Application - Zone System with Pumps (Primary/Secondary Piping)
Return filter
Not to exceed 4 pipe Dia or Max. 12"
System application drawings are intended to explain the system piping concept only.
Note
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Install a filter in the system return to remove foreign objects from the system. Foreign objects inside the system may result in
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abnormal system operation.
Refer to "3.3 Filling the System" on page 27 for make-up water connections and refer to the requirements of your local codes
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to ensure compliance.
Use a pump with an integral check valve or install a check valve at the pump outlet.
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Refer to "3.6.3 Wiring Diagram - Zone Pump System" on page 35 for wiring connections.
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Additional Zone
Air Separator
Boiler Pump
Zone #2
Zone #1
Backflow preventer
Pressure reducing valve
Expansion Tank
Make-up Water
Installing the System Piping 31