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The differential air pressure switch is a
safetydevicewhich will preventthe boiler
from firing if there is an air intake, boiler
heatexchangeror vent blockage.
1.Turn off serviceswitch,or lowerther-
mostatsetting.
2. Removevinylcapsfrom Tee.
3.Install t estinglinesas showntoinclined
manometer o rdifferential p ressure gauge
with the abilityto 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.
SERVICE
HINTS
This diagram
indicates the locations
of the connection
points required to check the differential air pressure.
DIFFERENTIAL AIR
PRESSURE S WITCHES
TRANSPARENT WHITE
SILICONE HOSE
SIGHT GLASS
"ESTING
UNES
MANOMETER
OSE
GAS VALVE
• 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.
Not Running
0"
3.5"
Closed
0.5"
Open
Running With-
1.00" for Model 125
3.5"
Closed
out Blockage
1.50" for Model 150
0.5"
Closed
(Approximate
min. vent
1.50" for Model 175
lengths)
2.00" for Model 200
Running With
' Greater Than or Equal
3.5"
Open
Blockage
To Setpoints
0.5"
Closed
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