56 Appendixes
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 “9.4
Setting the Operation Mode” on page 43.
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 9. 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 9. 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 2-stage D. MAX mode (refer to “9.4 Setting
the Operation Mode” on page 43). 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, death or substantial property damage.
Option 2. Using Digital Manometer
a. Open the offset pressure port by loosening the screw
two turns as shown in Figure 10.
Digital pressure
manometer
Figure 10. Connect Digital Pressure Monometer
b. Connect a manometer to the offset pressure port. For
dual port manometers, use the positive pressure side.
Model
Gas Type
Min Offset
Pa
NCB-24LSWE
G20
8 ± 1
G31
4 ± 1
NCB-28LSWE
G20
8 ± 1
G31
4 ± 1
NCB-34LSWE
G20
8 ± 1
G31
4 ± 1
NCB-40LSWE
G20
8 ± 1
G31
4 ± 1
Table 3. Offset value for minimum
Model
Gas type
G20
G31
[20 mbar]
[37 mbar]
Output
Consumption
Gas flow
Gas flow
Load
Kcal/h
kW
kW
m
3
/h
m
3
/h
NCB-24LSWE
Max.
16,770
19.5
20.0
2.142
0.804
Min.
3,552
4.1
4.2
0.450
0.169
NCB-28LSWE
Max.
20,124
23.4
24.0
2.570
0.964
Min.
3,522
4.1
4.2
0.450
0.169
NCB-34LSWE
Max.
24,317
28.3
29.0
3.106
1.165
Min.
4,276
5.0
5.1
0.546
0.205
NCB-40LSWE
Max.
28,509
33.2
34.0
3.641
1.366
Min.
3,354
3.9
4.0
0.428
0.161
