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5 60-2553—3
L8151A
OPERATION AND SETTINGS
Operation and Settings
HIGH LIMIT
The high limit opens and turns off the burner when the
water temperature reaches the setpoint. The high limit
automatically resets after the water temperature drops past
the setpoint and through the 10°F (6°C) differential.
WARNING
CAN CAUSE PROPERTY DAMAGE,
SEVERE INJURY OR DEATH.
Product is for use only in a system with a pressure
relief valve.
LOW LIMIT AND CIRCULATOR CONTROL
On a temperature rise, with the adjustable differential at
the minimum setting of 10°F (6°C), the low limit circuit
(RB) breaks and the circulator circuit (R-W) makes at the
control setpoint. On a temperature drop of 10°F (6°C)
below the setpoint, the R-B circuit makes and the R-W
circuit breaks.
Fig. 5—Typical hookup for the L8151A in a
multizone system.
L1
(HOT)
L2
1
2
3
3
4
4
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
CONTROL CASE MUST BE CONNECTED TO EARTH GROUND.
USE GROUNDING SCREW PROVIDED.
LINE VOLTAGE OIL BURNER CONTROL OR GAS VALVE.
B1 IS 1/4 IN. TAB TERMINAL.
M8885
T
T
ZC
ZR
B1
B2
C1
C2
1
2
G
THERMOSTAT
ZONE 1
THERM.
BURNER
CIRCULATOR
ZONE 1
LINE
HYDRONIC HEATING
CONTROL TERMINALS
2
1
4
3
5
6
R845A RELAY
TO ADDITIONAL
R845A RELAYS
FOR OTHER ZONES
THERMO-
STAT
ZONE 2
CIRCULATOR
ZONE 2
CIRC.
IF CONTROLLING TWO LOADS USE:
—TERMINALS 3 AND 4 FOR LINE
VOLTAGE LOAD.
—TERMINALS 5 AND 6 FOR LINE
OR LOW VOLTAGE LOAD.
Fig. 6—L8151A internal schematic.
21
T
T
1K
B2 B1
ZR
ZC
R
B
W
C1C2
1K1
HIGH LIMIT
1K2
LOW
LIMIT
CIRCULATOR
CONTROL
M8884
Fig. 7—Relationship of setpoints and differen-
tial.
LOW LIMIT
AND
CIRCULATOR
SETTING
HIGH LIMIT
SETTING
SWITCH BREAKS ON
TEMPERATURE RISE.
BURNER TURNS OFF.
CIRCULATOR OPERATES
ON A CALL FOR HEAT.
SWITCH MAKES ON
TEMPERATURE FALL.
BURNER OPERATES ON A
CALL FOR HEAT.
SWITCH MAKES R-W
AND BREAKS R-B ON
TEMPERATURE RISE.
SWITCH MAKES R-B AND
BREAKS R-W ON
TEMPERATURE FALL.
BURNER IS ON TO
MAINTAIN MINIMUM
WATER TEMPERATURE.
CIRCULATOR IS OFF.
110°F (43°C)
240°F (116°C)
M1523
SWITCH MAKES R-W
AND BREAKS R-B ON
TEMPERATURE RISE.
WHEN WATER REACHES PROPER TEMPERATURE, THE BURNER
SHUTS OFF OR THE CIRCULATOR PUMP STARTS (WHEN CALLING
FOR HEAT).
1
1
10°F (6°C)
DIFFERENTIAL
25°F (14°C)
DIFFERENTIAL
10°F (6°C)
DIFFERENTIAL
At any differential setting greater than 10°F (6°C), the
R-B make and R-W break temperatures remain the same
(control setting minus 10°F (6°C). The R-B break and R-W
make temperatures are the setpoint temperatures plus the
difference between the differential setting and 10°F (6°C).