AHRI APEX, Installation, Operating And Service Instructions

Page: 73 / 124

73
IX. System Start-up
(continued)
Table 24A: Approximate Throttle Screw
Adjustment Values from Fully Closed
Position, Natural Gas
Boiler
Model
Throttle Position (Number of Counter-
clockwise Turns from Fully Closed Position
APX425 4 & 3/4
APX525 4 & 3/4
APX625 6
APX725 10
APX825 7 & 1/2
Table 24B: Approximate Throttle Screw
Adjustment Values from Fully Closed
Position, LP Gas
Boiler
Model
Throttle Position (Number of Counter-
clockwise Turns from Fully Closed Position
APX425 3
APX525 3 & 3/4
APX625 6
APX725 10
APX825 7 & 1/2
1. Fully close throttle
by turning throttle screw
clockwise until it fully stops.
2. Open throttle screw
counter-clockwise the
number of full (360 degrees) and partial turns listed
in Table 24A for natural gas or Table 24B for LP
gas.
3. Follow instructions in Section L
“Perform
Combustion Test” to verify O
2
(or CO
2
) is within the
range specified in Table 21 for natural gas or Table
22 for LP gas at both high fire and low fire.
WARNING
The throttle adjustment values shown in Table
24A and Table 24B are approximate. The
final throttle setting must be found using a
combustion analyzer.
WARNING
Asphyxiation Hazard. If the throttle is very far out of adjustment on the “rich” (counter-clockwise) side,
the boiler burner may be running at 0% excess air or even with air deficiency. Operating the boiler in this
condition may cause property damage, personal injury or loss of life.
At 0% excess air the CO
2
readings will be either 11.9% CO
2
for natural gas or 13.8% CO
2
for LP gas (O
2
will
be 0%) and CO level will be extremely high (well over 1000 PPM).
If the burner operates with air deficiency, the following phenomena may be observed:
% CO
2
will actually drop (% O
2
will increase) as the throttle is turned counter-clockwise
% CO
2
will actually increase (% O
2
will drop) as the throttle is turned clockwise
If the boiler appears to operate with air deficiency, shut down the boiler and follow instructions in Paragraph
S “Correcting Throttle Screws Mis-Adjustment. Then, use a combustion analyzer to verify and adjust O
2
(or
CO
2
) and CO to values shown in Table 21 for natural gas or Table 22 for LP gas.