Navien NFB Series Installation & Operation Manual page 100

c. Activate multiple zones and set the boiler to operate at
1-stage MIN mode.
For operation mode selection, refer to "11.4.7
Note
Setting the Special Operation Modes" on page
95.
Measure the CO
2
If the CO value is not within 0.5% of the value listed in
2
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
the set screw no more than
counterclockwise to lower the CO
Figure 8. Set Screw Location
The set screw is located behind the screw-on
Note
cover. This must be removed first.
d. Activate multiple zones and set the boiler to operate at
2-stage D. MAX mode (refer to "11.4.7 Setting the Special
Operation Modes" on page 95). Measure the CO
at high fire.
If the CO values do not match Table 2 at high fire, do not
2
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.
100 Appendixes
value at low fire.
/ in or 4 mm Allen wrench, turn
5
32
/ turn clockwise to raise or
1
4
value.
2
Option 2. Using Digital Manometer
a. Open the offset pressure port by loosening the screw two
turns as shown in Figure 9.
Figure 9. Connect Digital Pressure Monometer
b. Connect a manometer to the offset pressure port. For dual
port manometers, use the positive pressure side.
Model
NFB-175
NFB-200
value
2
Digital pressure
manometer
Kit Part No. Gas Type
NAC-N175 NG -0.04 in ±0.01 in
NAC-L175 LP -0.02 in ±0.01 in
NAC-N200 NG -0.04 in ±0.01 in
NAC-L200 LP -0.02 in ±0.01 in
Table 3. Offset value for low fire
Offset