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• Following steps and diagram indicate locations of
connection points required to check differential air
pressure.
• Differential air pressure switch is safety device which
prevents boiler from fi ring if there is air intake, boiler
heat exchanger or vent blockage.
• Turn off service switch, or lower thermostat setting.
• Remove vinyl caps from Tee and 4-way connector.
• Install testing lines as shown to inclined manometer or
differential pressure gauge with ability to read 0.01” to
3.0” w.c.
• Turn on service switch and set thermostat to call for
heat.
BOILER
STATUS
DIFFERENTIAL
PRESSURE (W.C.)
PRESSURE
SWITCH
CONNECTS
Not Running 0” Normally Open
Setpoint
1.00” for Model-100
1.60” for Model-75
2.10” for Model-50
Running
Without
Blockage
Greater Than
Setpoints
Closed
Running
With
Blockage
Less Than or Equal to
Setpoints
Open
If manometer readings do not correspond to chart above,
check for possible causes:
• - Blockage or moisture in suction lines
• - Blockage in air intake or vent pipes
• - Undersized air intake or vent pipes
• - Loose blower wheel or motor shaft
• - Incorrect pressure switch or pressure switch setpoint
When pressure reading is proper and the pressure switch is
operating properly, remove testing lines and reinstall vinyl
caps to Tee and 4-way connector.
DIFFERENTIAL AIR PRESSURE SWITCH CHECK