SG Series Boilers – Installation and Service Manual
12
1.7 BC-1 CONTROLLER (FOR 2 STAGE BOILERS ONLY)
WARNING
For boilers equipped with the BC-1 Controller, read all instructions in this manual and the BC-1
Controller Manual before placing the boiler in operation or making adjustments to the
controller. Adjustments must be made by a qualified heating technician.
The BC-1 controller is supplied as standard option with two stage boilers for models SG-315 and larger.
It is not supplied with boilers equipped with a full modulating gas valve. For convenience, the BC-1
controller is factory wired to terminal block TB4 and ready for field wiring connections. The field wiring to
TB4 is determined based on the operating mode selected (i.e. mode 1 to 6), the heating application and
the piping arrangement (i.e. parallel or primary/secondary). Refer to Figure 2 for the wiring diagram
according to each mode. For important instructions regarding programming and operation of the BC-1
controller, refer to the BC-1 Controller Manual included with your boiler.
Power Outputs from BC-1:
Boiler Stage outputs from 15-STG1 and 17-STG2
terminals from the BC-1 are 24 Vac, 60 Hz (when
factory wired).
Figure 2 – BC-1 Controller
Alarm output from 23-ALARM terminal from the BC-1 is
24 Vac, 60 Hz, 0.45 A maximum (when factory wired).
Alarm is wired to terminal block TB4, terminals AL&AL.
Signal Inputs (Do not apply external power):
The following signal inputs are located on terminal block TB4:
HT&R: Room thermostat or zone valve end switch,
24Vac switching input, closed is activation.
ST&R: Setpoint DHW aquastat, 24Vac switching
input, closed is activation.
FS&FS: Flow switch, 24Vac switching input, closed
is activation.
Thermistor Sensors
BO&CM: Boiler outlet sensor
BI&CM: Boiler inlet sensor
OS&CM: Outdoor sensor
SD&CM: Supply / DHW sensor
BC-1 Controller Mounting
The BC-1 controller mounts on separate bracket on the control panel using a sheet metal screw at the top
center. To remove the controller: 1.) remove the front casing panel, 2.) pull off the black top cover of the
controller, 3.) unscrew the sheet metal screw, 4.) lift the controller slightly out of the rectangular cutout in
the mounting bracket, 5.) pull off the Molex connector while simultaneously holding down the tab on the
left side.
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