INSTRUCTION MANUAL
MM-243D
2
Approximate
Distance Above
Cast Line
Differential
Setting
In. (mm)
In. (mm)
Pump Off
1
3
/
8
(35)
3
/
4
(19)
Pump On
5
/
8
(16)
Burner On
7
/
8
(22)
7
/
8
(22)
Burner Off
0
(0)
NORMAL BOILER
WATER LINE
PUMP
OFF
BURNER
OFF
BURNER
“CUT-OFF LEVEL”
AT CAST LINE
1 3/8" (35mm)
CUT-OFF
LEVEL
NORMAL BOILER
WATER LINE
CUT-OFF
LEVEL
PUMP OFF
PUMP ON
3/4" (19mm)
OPERATION
Maximum Pressure:
50 psi (3.5 kg/cm
2
)
Electrical Ratings
Settings and Differential Pressures
Values are ±
8
” (3.2mm).
Series 42S
50 psi
(3.5 kg/
cm
2
)
Pressure
Pump Circuit Rating (Amperes)
Voltage
Full Load
Locked Rotor
Pilot Duty
120 VAC
7.4
44.4
345 VA at
240 VAC
3.7
22.2
120 or 240 VAC
NORMAL BOILER
WATER LINE
BURNER
CUT-OFF LEVEL
AT CAST LINE
7/8" (22 mm)
BURNER ON
BURNER OFF
CUT-OFF
LEVEL
Motor Horsepower
Voltage
Hp
120 VAC
1/3
240 VAC
1/3
• Before using this product read and understand instructions.
• Save these instructions for future reference.
• All work must be performed by qualified personnel trained in the proper application, instal-
lation, and maintenance of plumbing, steam, and electrical equipment and/or systems in
accordance with all applicable codes and ordinances.
• To prevent serious burns, the boiler must be cooled to 80˚F (27˚C) and the pressure must be
0 psi (0 bar) before servicing.
• To prevent electrical shock, turn off the electrical power before making electrical connections.
• This low water cut-off must be installed in series with all other limit and operating controls
installed on the boiler. After installation, check for proper operation of all of the limit and
operating controls, before leaving the site.
• To prevent serious personal injury from steam blow down, connect a drain pipe to the
control opening to avoid exposure to steam discharge.
• To prevent a fire, do not use this low water cut-off to switch currents over 7.4A, 1/3 Hp at
120 VAC or 3.7A, 1/3 Hp at 240 VAC, unless a starter or relay is used in conjunction with it.
Failure to follow this warning could cause property damage, personal injury or death.
WAR
NING
CAUT
ION
!
WARNING
Replacement Head Mechanism
Replacement head mechanisms can be installed without
disturbing existing equalizing connections or disassembly
of components, making repairs simple and easy.
Replacement Head Mechanism
42S-HD
(Snap Switch)
