Navien NPE Installation & Operation Manual page 48

2. On the slave water heater, press and hold the Diagnostics and
Down [-] buttons for more than 2 seconds. "SL.01" will appear
on the display to confirm that this water heater is set as a slave.
3. Repeat step 2 to configure the rest of the slave water heaters in
the system.
4. On the master water heater, press and hold the Diagnostics
and Up [-] buttons for more than 5 seconds. All the display
screens on the configured water heaters will return to the
temperature display.
To add additional slaves at a later time, repeat step
Note
2.
To cancel the cascade communication setup, on the
master water heater, press and hold the Diagnostics
and Reset buttons for more than 5 seconds. The
water heaters will revert to independent operation.
Repeat steps 1-4 to reassign the master water
heater.
48 Installing a Cascade System