![background image](http://html2.mh-extra.com/html/navien/nfc-250-175h/nfc-250-175h_installation-manual_3727065135.webp)
135
Appendixes
c. Activate multiple zones and set the boiler
to operate at 1-stage MIN mode (refer
to “11.6.7 Setting the Special Operation
Modes” on page 126). Measure the offset
value at low fire and compare it to the
values in Table 3. If the offset value is out of
range, the gas valve set screw will need to
be adjusted.
If adjustment is necessary, locate the set
screw as shown in Figure 10. Using a
5
/
32
in
or 4mm Allen wrench, turn the set screw
no more than
1
/
4
turn clockwise to raise or
counterclockwise to lower the offset value.
Figure 10. Set Screw Location
Note
The set screw is located behind
the screw-on cover. This must be
removed first.
d. At high fire, do not check the offset value
and never adjust the gas valve.
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
NFC-
250/200H
NFC-
250/175H
0-
5,399 ft
NAC-
NC250/200H Natural
Gas
-0.03 in ±
0.01 in
5,400-
10,100 ft
NAC-
NCH250/200H
0-
10,100 ft
NAC-
LC250/200H
Propane
Gas
-0.02 in ±
0.01 in
Table 3. Offset value for low fire
Summary of Contents for NFC-250/175H
Page 67: ...67 Venting for Combustion Air WARNING The vent installation detector Detectable Undetectable...
Page 149: ...Memo...
Page 150: ......