Navien NFC-175 Installation & Operation Manual page 66

If Recirculation Return Line Is Not Installed
Install a NaviCirc valve at the furthest fixture from the water heaters and connect a by-pass line on the 1st NPE "A" unit as illustrated below.
Refer to the NaviCirc and NPE Installation Manuals for additional details. The NFC boiler should be set to Combi Pre-heat Mode.
Pressure
Relief Valve
Heating
Supply
Pump
Air Separator with
Expansion Tank
Optional System
Temperature Sensors
Heating Return
Note
A HotButton cannot be used for cascade systems.
66 Installing a Cascade System
Air Vent
Hydronic
Feed
Expansion
Water
Tank
Pressure
Relief Valve
Solenoid
NaviClean
valve
<NPE-A> <NPE-S>
Sub1 Sub2
Domestic Hot Water Supply
<NPE-S>
Sub3
Ball Valve
Check
Faucet
Domestic
Valve
Cold Water
Supply