Navien NCB-20LHWE, Installation & Operation Manual

Page: 67 / 80

Model
Gas type
G20 G31
[20 mbar] [37 mbar]
w o lf s a G w o lf s a G n o it p m u s n o C t u p t u O
Load Kcal/h kW kW m
3
/h m
3
/h
NCB-20LHWE
Max. 16,770 19.5 20.0 2.142 0.804
Min. 3,354 3.9 4.2 0.450 0.169
NCB-23LHWE
Max. 20,124 23.4 24.0 2.570 0.964
Min. 3,354 3.9 4.2 0.450 0.169
NCB-28LHWE
Max. 24,317 28.3 29.0 3.106 1.165
Min. 4,214 4.9 5.1 0.546 0.205
NCB-33LHWE
Max. 28,509 33.2 34.0 3.641 1.366
Min. 3,268 3.8 4.0 0.428 0.161
c. Fully open several hot water fixtures and set the boiler
to operate at 1-stage MIN mode.
Note
For operation mode selection, refer to “11.4
Setting the Operation Mode” on page 47.
Measure the CO
2
value at low fire.
If the CO
2
value is not within 0.5% of the value listed in
Table 2, the gas valve set screw will need to be adjusted.
If adjustment is necessary, locate the set screw as shown
in Figure 8. Using a 5 /
32
in or 4 mm Allen wrench, turn
the set screw no more than
1
/
4
turn clockwise to raise or
counterclockwise to lower the CO
2
value.
Figure 8. Set Screw Location
Note
The set screw is located behind the screw-on
cover. This must be removed first.
d. Fully open several hot water fixtures and set the boiler to
operate at C.MAX (20/23/28LHWE) or C.MAX2(33LHWE)
mode (refer to “11.4 Setting the Operation Mode” on
page 47). Measure the CO
2
value at high fire.
If the CO
2
values do not match Table 2 at high fire,
do not adjust the gas valve. Check for the proper Gas
Orifice.
DANGER
Improper gas valve settings can cause severe personal injury
or substantial property damage.
4. Using a Phillips screwdriver, remove four screws (two at the
bottom and two at the top) of the front cover assembly to
gain access to the internal components.
5. Once the front cover is removed, place it in a safe location to
prevent accidental damage.
6. Loosen the four screws holding the front panel and remove
the front panel.
Note
When removing the front panel, label all wires and
make sure all wires are disconnected.
13.2 Cleaning the Heat Exchanger
WARNING
Before cleaning the heat exchanger, make sure the boiler is
off.
To properly maintain the boiler, you should clean the heat
exchanger annually.
To clean the heat exchanger:
1. Press the Power button on the front panel to turn off the
boiler.
2. Disconnect the power supply to the boiler.
3. Turn off both gas and water supply to the boiler.
Note
Wait at least 30 minutes for the heat exchanger to
cool down.
67 Appendices