Navien NFB-175H User's Information Manual page 21

Before flushing the heat exchanger,
Note
additional flush valves ("A" and "B") must
be installed on the near boiler piping
(included with Navien Manifold System).
A
C
To flush the Heat Exchanger:
A
System
Supply
C
Circulation Pump
B
D
Navien
Manifold
System
B
Pump in
Manifold
System
D
System
Return
1. Press the Power button (
to turn off the boiler.
2. Disconnect the power supply to the boiler.
3. Close the "C" and "D" valves on the supply and
return water lines.
4. Connect one tube to the "A" valve and place the
free end in the bucket.
5. Connect one of the tubes to the circulation
pump outlet and the return water line at the "B"
valve.
6. Connect one tube to the circulation pump inlet
and place the free end in the bucket.
7. Pour the cleaning solution into the bucket.
8. Open both "A" and "B" valves.
9. Turn on the circulation pump and allow the
solution to circulate through the boiler. Refer
to the manufacturer's literature for information
about the circulation time.
10. Rinse the cleaning solution from the boiler:
a. Remove the free end of the drain tube from
the bucket and place it in the condensate
drain or laundry tub (wherever the boiler
drains).
b. Close the "B" valve and open the "D" valve. Do
not open the "D" valve yet.
c. Allow water to flow through the boiler for
5 minutes.
d. Close the "A" valve and open the "C" valve.
11. Disconnect all tubes and valves.
12. Reconnect the power supply to the boiler.
13. Press the Power button (
to turn on the boiler.
) on the front panel
) on the front panel
Maintaining the Boiler 21