2
W
B
R
X
X
T
1
4
3
T
X
X
2
2
WIRING
All wiring should be done in accordance with local and national electrical codes and ordinances.
If the manufacturer of the heating or cooling equipment
has recommended a wiring diagram, follow his
instructions. If none are available, the diagram shown on
this page will suffice for general applications. For hot
water heating, refer to the typical diagrams presented
below.
DIAGRAM FOR BOILER WITH TANKLESS
DOMESTIC COIL
The R-B contacts of the low limit-circulator control maintain
domestic hot water at the desired temperature year-
round.
When the thermostat calls for heat, the burner starts. The
circulator also starts if the R-W contacts of the low limit-
circulator control are closed.
If excessive boiler temperature causes the high limit to
open, the circulator continues to run but the burner shuts
down until the high limit recloses.
If low boiler temperature causes the R-W contacts of the
low-limit circulator control to open, the burner stays on
but the circulator stops until the R-W contacts reclose.
When the thermostat is satisfied, the circulator stops.
The burner also shuts down if the R-B contacts of the low
limit-circulator control are open.
DIAGRAM FOR BOILER WITHOUT DOMESTIC COIL
When the thermostat calls for heat, the burner starts. The
circulator also starts if boiler temperature is above setting
of circulator control.
If excessive boiler temperature causes high limit to open,
the circulator continues to run but the burner shuts down
until the high limit recloses.
When low boiler temperature causes circulator control to
open, the burner stays on but the circulator stops until the
circulator control recloses. When thermostat is satisfied,
both burner and circulator stop.
DIAGRAM FOR BOILER WITHOUT DOMESTIC COIL
When the thermostat calls for heat, the burner starts. The
circulator also starts if boiler temperature is above setting
of circulator control.
If excessive boiler temperature causes high limit to open,
the circulator continues to run but the burner shuts down
until the high limit recloses.
When low boiler temperature causes circulator control to
open, the burner stays on but the circulator stops until the
circulator control recloses. When thermostat is satisfied,
both burner and circulator stop.
X
X
T
1
4
3
T
X
X
2
2
24 VAC
GAS VALVE
X
X
Fig. 3a & 4a Diagram for
Gas-Fired System
HIGH LIMIT
TRANS
.
Fig. 3
Fig. 2
T
1
4
– 2 –
3
T
X
X
LOAD #2
LOAD #1
LOW VOLTAGE
2-WIRE
THERMOSTAT
AUXILIARY TO LOW
OR MILLIVOLTAGE
(POWER PILE) LOAD
FOR 120V. LOADS:
Connect this line to
neutral (grounded) side of 120V. line
or terminal #2 on relay.
FOR 240V. LOADS:
Connect load to L2
(hot line of 120/240 3-wire line,
NOT connected to terminal #1).
terminal #2 MUST BE connected to
neutral (ground) line.
INTERNAL
WIRING
IGNITION
TRANS.
BURNER
MOTOR
CIRCULATOR
MOTOR
CIRCULATOR
CONTROL
HIGH
LIMIT
TO AUXILIARY LOAD
(IF USED)
THERMOSTAT
INTERNAL
WIRING
TYPE 668 OIL
BURNER CONTROL
(LINE VOLTAGE)
JUMPER
L1
LINE
N
THERMOSTAT
TO AUXILIARY LOAD
(IF USED)
HIGH
LIMIT
LOW LIMIT
CIRCULATOR
JUMPER
CIRCULATOR
MOTOR
BURNER
MOTOR
IGNITION
TRANS.
TYPE 668 OIL
BURNER CONTROL
(LINE VOLTAGE)
L1
LINE
N
INTERNAL
WIRING
Fig. 4
Fig. 5 Diagram for Millivolt Gas-Fired
System and line voltage circulator
T
1
4
3
T
X
X
2
2
TH
TH PG
PG
TO AUXILIARY LOAD
(IF USED)
CIRCULATOR
CONTROL
CIRCULATOR
MOTOR
L1
LINE
N
750 MV
POWER
GENERATOR
INTERNAL
WIRING
750 MV
GAS VALVE
HIGH LIMIT
THERMOSTAT
N
LINE
L1
MUST BE N.E.C.
CLASS 1
WIRING