122 Appendixes
d. Activate multiple zones and set the boiler
to operate at 2-stage D. MAX mode (refer
to “11.6.7 Setting the Special Operation
Modes” on page 114). 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 9.
Digital pressure
manometer
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 Altitude
Kit Part No. Gas Type Offset
NFB-
175H
0-5,399 ft NAC-N175H
Natural
Gas
-0.03 in
±0.01 in
5,400-
10,100 ft NAC-NH175H
0-10,100 ft NAC-L175H Propane
Gas
-0.02 in
±0.01 in
NFB-
200H
0-5,399 ft NAC-N200H
Natural
Gas
-0.03 in
±0.01 in
5,400-
10,100 ft NAC-NH200H
0-10,100 ft NAC-L200H Propane
Gas
-0.02 in
±0.01 in
Table 3. Offset value for low fire
Model Altitude
Fuel
High fire
Low fire
%CO
2
%CO
2
NFB-
175H
NFB-
200H
0-5,399 ft
Natural
Gas
8.8
8.9
Propane
Gas
10.5
10.7
5,400-
10,100 ft
Natural
Gas
8.8
8.9
Propane
Gas
10.5
10.7
Table 2. CO
2
value
(CO
2
values must be within 0.5% of the
values listed.)
c. Activate multiple zones and set the boiler to
operate at 1-stage MIN mode.
Note
For operation mode selection,
refer to “11.6.7 Setting the
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.
Summary of Contents for NFB-175H
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