38
P/N 42-9470 11/07 Copyright 2007 Mestek, Inc.
Cast iron condensing boiler
Cast iron condensing boiler
— Installation and operation manual
Figure 29
Throttle adjustment and fl ame window
Adjust gas valve throttle setting
Allow combustion to stabilize
Allow the boiler to operate 15 minutes, or as needed to obtain a steady reading on
the analyzer.
If the fl ame or burner surface appear red, NO NOT allow the boiler
to run without adjusting the gas valve thrott le to reduce fuel input as
described below. Proceed with fi nal thrott le sett ing only if the fl ame is
visually acceptable (blue and steady).
Acceptable CO
2
/O
2
values
Th
e CO
2
/O
2
values must be within the limits given in Table 5. Th
e fl ame must be blue
and steady as discussed on page 37. CO must be no higher than 50 ppm.
Table 5
Acceptable CO
2
and O
2
values
Natural gas – High fi re
CO
2
/ O
2
Natural gas – Low fi re
CO
2
/ O
2
Minimum %
8.4 / 6.2
Minimum %
7.5 / 7.8
Maximum %
9.5 / 4.2
Maximum %
8.2 / 6.5
Propane – High fi re
CO
2
/ O
2
Propane – Low fi re
CO
2
/ O
2
Minimum %
9.3 / 6.2
Minimum %
8.2 / 7.8
Maximum %
10.7 / 4.2
Maximum %
9.1 / 6.5
Adjusting gas input with throttle screw - max input
Adjust gas input with the thrott le screw adjustment using a long-shank common
bit screwdriver inserted through the hole in the jacket top. (Figure 29)
When adjusting the thrott le sett ing, make changes in half-turn increments. Allow
the fl ame to stabilize before adjusting each time. (Reduce gas input if the fl ame or
burner appears red.)
If CO
2
is too
HIGH
(O
2
too low):
REDUCE
gas by turning the adjustment
CLOCKWISE
(one half turn at a
time). Recheck the analyzer and fl ame aft er each half turn.
4. If
CO
2
is too
LOW
(O
2
too high):
INCREASE
gas by turning the adjustment
COUNTERCLOCKWISE
(one
half turn at a time). Recheck the analyzer and fl ame aft er each half turn.
Verify gas inlet pressure
With the boiler operating at high fi re, check the gas pressure at the manual gas
valve. Gas pressure should never fall off by more than 2 inches w.c. (50 mm).
To meter gas input (natural gas only):
Meter gas input with the high-fi re jumper in place.
Turn off all other gas appliances that use the same gas meter as the boiler.
Call your gas supplier and ask for the heating value of the gas (Btu per cubic foot).
Start the boiler and let it run for 15 minutes (high-fi re jumper in place).
With the boiler operating, clock the time in
SECONDS
that it takes to burn
10
cubic feet of gas at high fi re.
Insert the heating value and the time, in seconds, into the formula below.
Input = [
Gas Btu per cubic foot
] x [
3600
] x [
10
] ÷ [
seconds
]
7. If the computed rate exceeds the desired input rate or 200,000 Btuh, reduce the gas
input with the gas thrott le adjustment.
•
•
1.
2.
3.
•
•
1.
1.
2.
3.
4.
5.
6.
Starting the boiler
(continued)
Never operate the boiler at an input higher than
its rating. Excess input can result in overheating
and damage to the heat exchanger and boiler
components.
Check low fi re operation
.
Turn the boiler on/off switch
OFF
.
Remove the high-fi re contact jumper. Connect the jumper
wire across the low-fi re terminals of the connector board
(Figure 28, page 37). Th ese terminals are located on the
lower row as shown.
Turn the boiler on/off switch
ON
.
Th e boiler will start at about 30% of input and then move to
the low fi re condition.
Make sure the fl ame is blue and steady, NOT red or light
blue and unsteady.
If the fl ame or burner appears red, or if the CO
2
or O
2
are
outside the ranges of Table 5, turn the boiler on/off switch
OFF
.
See the next page for instructions to adjust the gas valve
low-fi re sett ing.
If fl ame and CO
2
/O
2
/CO are acceptable, proceed with set-
up (page 40) —
No further gas valve adjustments
are needed
. Replace the gas valve cover plate. Remove the
low-fi re jumper and replace the electrical panel cover.
Changing from propane to natural gas or
natural gas to propane
— When adjusting
the boiler for a diff erent gas, the low-fi re gas
adjustment must be changed using the procedure
on page 39.
1.
2.
3.
4.
5.
6.
7.
8.
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