Install Instructions

Installation & Service Manual
37
5 Electrical connections (continued)
Minimum Set Point (High Outdoor Air Temperature)
If the inlet sensor is used to determine set point, the
minimum set point is fixed at 140°F (60°C). If a system
sensor is used the range of this parameter is 110°F (43°C) to
140°F (60°C) and can be adjusted using the middle knob on
the temperature controller. The two-stage thermostat will
apply the outdoor air reset set point to the system sensor,
while also applying a fixed 140°F (60°C) set point to the inlet
sensor. If inlet water temperature drops below 140°F (60°C)
the temperature controller will force the boiler to high fire.
Requiring a minimum 140°F (60°C) inlet water temperature
will help prevent problems with condensation. For systems
requiring return temperatures less than 140°F (60°C), a
bypass must be installed. Reference Low Temperature Bypass
Requirements for additional information.
High Fire Offset
The temperature controller operates a two-stage firing system,
which enables the boiler to start on low fire and continue on
to high fire when there is a greater heat demand. High fire
operates all burners at full rate, while low fire operates the
burners at approximately one-half rate. Operating at high fire
only when extra capacity is needed increases overall system
efficiency. The High Fire Offset knob specifies the number
of degrees below boiler 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 temperature settings between 0°F and 20°F.
If the control is set above 0°F, the high fire delay will be 120
seconds. If the control is set to 0°F, the high fire offset is
disabled and the unit will operate at high fire until the set
point is reached.
Differential
The differential specifies the number of degrees below the set
point the control will allow the water temperature to drop
before it brings the unit back on again. The differential is
factory set at 12°F (7°C).
Temperature Control Sensors
The two-stage temperature control regulates the burner
ignition and pump functions, and can measure up to four (4)
different sensor inputs. Standard boiler units are equipped
with an inlet water temperature sensor and an outside air
temperature sensor. A system sensor is also provided for
use as a remote sensor. If this sensor is connected to the
control board, the boiler will operate based on system water
temperature set point. A field supplied tank Aquastat may
also be used for water heating applications. The four available
sensor inputs are as follows:
1. Inlet Water Temperature Sensor
2. System Sensor
3. Outside Air Temperature Sensor
4. Tank Aquastat
Inlet Water Temperature Sensor
This sensor measures the inlet water temperature coming into
the unit. The inlet water temperature sensor is placed into
the inlet bulbwell on the boiler. This sensor is installed by the
factory in new units and should not be removed. A fixed 140°F
minimum set point is applied to this sensor.
System Sensor
This sensor can be used as a remote system sensor in a boiler
system. When this sensor is connected the temperature control
applies the outdoor air reset set point to the system sensor
and a minimum 140°F set point to the inlet sensor. Systems
requiring return temperatures less than 140°F should install a
low temperature bypass. A bypass allows the unit to operate
at a lower system set point, while maintaining the minimum
inlet water temperature. Connect the system sensor to the SYS/
TANK contacts on the control board. For more information,
reference the Installation of System Sensor section on page 38.
Outdoor Air Temperature Sensor
This sensor ties boiler operating set point to the outdoor air
temperature. As outdoor temperatures drop and there is greater
heat demand, the control will increase the temperature setting
of the boiler. The boiler set point will decrease as outdoor
temperatures rise, resulting in more energy efficient operation.
The sensor comes with a housing that helps protect the sensor
from the elements. Mount the air sensor housing outdoors,
under the eve of the roof. Make sure the housing is out of direct
sunlight. This will ensure that the sensor will accurately read the
true outdoor temperature. Connect the outdoor air temperature
sensor to the terminal block on the upper temperature control
board. In the event the outdoor air sensor is not functioning,
the temperature control will indicate a fault with a flashing red
light and the boiler set point will default to Maximum Set Point.
For more information on wiring the sensor, see Wiring of the
Outdoor Air Sensor on page 38.
Tank Aquastat
An indirect water heater can be connected to the boiler with a
field supplied Aquastat. When there is a water heating demand
the temperature control will increase boiler set point to 180°F
(82°C). Follow the manufacturer’s instructions supplied with
the Aquastat for proper installation and adjustment. Determine
the location of the tank and measure the amount of wire needed
to connect the Aquastat to the control. Reference the terminal
strip wiring chart (Table 5A) to determine maximum allowable
length and wire gauge recommended. Ensure all wire insulation
is trimmed to reveal at least 3/8" of exposed wire. Feed the wires
through the access hole located on the side of the unit and secure
the connectors to the Tank Aquastat terminal block CN10 on
the upper temperature control board. Reference the Wiring of
Outdoor Air Sensor section for additional wiring guidelines.