Navien NCB300-28K, Service Manual

Page: 26 / 108

System Details 25
c. Fully open several hot water fixtures and set the boiler
to operate. 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 T15 Hexalobular 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. After Gas Setup Wizard is done, operate at minimum mode.
Note
For operation mode selection, refer to “4.4.7.3
Setting the Special Operation Modes” on
page 34.
e. Fully open several hot water fixtures and set the boiler
to operate at DHW maximum mode (refer to “4.4.7.3
Setting the Special Operation Modes” on page 34).
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.
14. Turn on the gas and water supply to the boiler.
15. Measure and adjust the gas/air ratio.
a. Loosen the screw, rotate the plate and remove the
gasket to access the emissions monitoring port as
shown in Figure 7.
b. Insert the analyser into the port (Figure 7).
White Cap
(Air Supply)
Black Cap
(Exhaust Gas)
Figure 7. Insert the Analyser
Model Gas Type
Max Min
%CO
2
%CO
2
NCB300
G20 8.80 % 8.35 %
G31 10.25 % 10.10 %
Table 2. CO
2
Value
(CO
2
values for high fire must be within 0.5% and CO
2
values
for low fire must be within 0.3% of the values listed.)
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
NCB300-28K
Max. 20,640 24.0 24.7 2.645 0.252
Min. 3,700 4.2 4.3 1.775 0.169
NCB300-37K
NCB300-41K
Max. 22,360 26.0 26.8 2.870 0.273
Min. 3,870 4.5 4.6 1.944 0.185