Hydronic Heating Boilers and Domestic Water Heaters Installation and Service Manual

High-Fire Offset
The temperature control operates a two-stage firing system.
The two stages are High-Fire and Low-Fire. High-Fire
operates all burners while Low-Fire operates approximately
one-half of the burners.
The High-Fire knob specifies the number of degrees below set
point that the High-Fire stage shuts down. At that point, the
unit will continue to operate at the Low-Fire stage until the set
point is reached.
The High-Fire offset knob has settings between 0°F and 20°F.
If set at 0°F, the High-Fire offset is disabled and the unit will
operate at the High-Fire stage until the set point is reached and
the temperature control shuts the unit off.
When the High-Fire offset knob is set to 0 or 1, the unit will
light at Low Fire and operate for approximately 10 seconds
before the High-Fire stage actuates. When set to 2 or above,
the unit will operate at Low Fire for 2 minutes before the High
Fire stage actuates.
Outdoor Air Reset Option
For boilers ordered with the Outdoor Air Reset option, there is
an additional control (see Figure 36). There are three setting
knobs for Shutdown, Outdoor Air Max., and Ratio. There is
also a switch to turn the outdoor air sensor On or Off. An O.A.
Sensor is also included.
Shutdown
The Shutdown knob specifies the outdoor air lockout
temperature at which the control would prevent the unit from
operating. This feature can be enabled/disabled with the O.A.
Shutdown switch.
Outdoor Air Max (O.A. Max)
The O. A. Max knob allows a reset up to the maximum outdoor
air temperature specified by this knob setting. When the
outdoor air temperature is above the specified setting, the unit
will not function in the O.A. Reset Mode, but will continue to
run at the selected set point temperature.
Note that the set point knob will now indicate the “minimum”
boiler temperature. Target temperature is determined by the
ratio and outdoor air temperature below the O.A. Max setting.
Ratio
The Ratio knob allows the control over the reset ratio to be
used during Outdoor Air Reset. The allowable ratios are as low
as 0.5:1 or as high as 1.5:1.
Selecting the 0.5:1 ratio will increase the set point 0.5°F for
every 1.0°F drop in outdoor air temperature up to the
maximum set point temperature.
Selecting the 1.5:1 ratio will increase the set point 1.5°F for
every 1.0°F drop in outdoor air temperature up to the
maximum set point temperature.
See Figure 37 for an outdoor air reset chart example.
Figure 36 - Optional Outdoor Air Reset Control
Installation and
Service Manual
31
R4
R4
R6
R6
R8
R8
R16
R16
R15
R15
C7
C7
C9
C9
C10
C10
VR2
VR2
VR3
VR3
OJ1
OJ1
OJ2
OJ2
D4
D4
J4
J4
CN1
CN1
CN2
CN2
CN9
CN9
CN7
CN7
CN8
CN8
CN3
CN3
CN4
CN4
CN5
CN5
CN6
CN6
W1
W1
TST2314
TST2314
20
20
15
15
10
10
5
5
(F-)0
(F-)0
15
15
14
14
13
13
12
12
11
11
10
9
9
8
8
7
7
6
6
5
5
OFF
OFF
120
120
240
240
220
220
200
200
160
160
140
140
SETPOINT
SETPOINT
DIFFERENTIAL
DIFFERENTIAL
HIGH-FIRE
HIGH-FIRE
OFFSET
OFFSET
(c)2002 L.C.
(c)2002 L.C.
SHUTDOWN
45
50
45
1.3
O.A. MAX.
70
40
VR1
65
RATIO
VR2
0.6
0.5
0.7
1.4
1.5
W1 W2
W3
60
50
7040
55
60
VR3
65
DISABLE
O.A. SHUTDOWN
1.0
0.9
0.8
1.2
1.1
O.A. SENSOR
ENABLE
ON
SW1
55
CN1