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DETAILED SEQUENCE OF OPERATION
The differential air pressure switch is a
safety device which will prevent the boiler
from firing if there is an air intake, boiler
heat exchanger or vent blockage.
1. Turn off service switch, or lower ther-
mostat setting.
2. Remove vinyl caps from Tee.
3. Install testing lines as shown to inclined
manometer or differential pressure gauge
with the ability to read 0.01” to at least
6.0” w.c.
4. Turn on service switch and set ther-
mostat to call for heat.
5. If manometer readings do not corre-
spond to the chart at right, check for
possible causes:
• Blockage or moisture in suction
lines to switch.
• Blockage or moisture in orifice in-
stalled in suction lines to switch.
• Blockage in air intake or vent
pipes.
• Undersized air intake or vent
pipes.
• Loose blower wheel on motor
shaft.
• Incorrect pressure switch or pres-
sure switch setpoint.
• Gas valve out of adjustment.
6. When pressure reading is proper and
the pressure switch is operating prop-
erly, remove testing lines and reinstall
vinyl caps to Tee and 3-way connector.
Boiler Status
Differential Pressure Switch Contacts
Not Running
0”
3.5”
Closed
0.5”
Open
Running With-
out Blockage
(Approximate
min. vent
lengths)
1.00” for Model 125
3.5”
Closed
1.50” for Model 150
0.5”
Closed
1.50” for Model 175
2.00” for Model 200
Running With
Blockage
Greater Than or Equal
To Setpoints
3.5”
Open
0.5”
Closed
This diagram indicates the locations of the connection
points required to check the differential air pressure.
SERVICE HINTS
ORANGE SILICONE HOSE
MANOMETER
TESTING
LINES
DIFFERENTIAL AIR
PRESSURE SWITCHES
TRANSPARENT WHITE
SILICONE HOSE
