46
NEGATIVE PRESSURE SWITCH CHECK
BOILER
STATUS
NEGATIVE
PRESSURE (W.C.)
PRESSURE
SWITCH
CONNECTS
Not Running
0”
Normally
Closed
Setpoint
-0.50”
for Models 100 & 075
Running
Without
Blockage
Less Negative than
Setpoint
Closed
Running
With
Blockage
More Negative than
Setpoint
Open
To Gas Valve Vent
For use on Model - 100 boilers only.
• Following steps and diagram indicate locations of
connection points required to check negative pressure.
• Negative pressure switch is safety device which
prevents boiler from firing if there is air intake
blockage.
• Turn off service switch, or lower thermostat setting.
• Remove vinyl cap from 4-way connector.
• Install test line as shown to inclined manometer or
differential pressure gauge with ability to read 0.01” to
5.0” w.c.
• Turn on service switch and set thermostat to call for
heat.
• If manometer readings do not correspond to chart,
check for possible causes:
A. Blockage in air intake
B. Undersized air intake
C. Loose blower wheel or motor shaft
D. Incorrect pressure switch or pressure switch
setpoint
• When pressure reading is correct and the pressure
switch is operating properly, remove test line and
reinstall vinyl cap to 4-way connector.
Negative Pressure Switch
Differential Air Pressure Switch
Red Transparent Vinyl Tubing
Tee
Vinyl Cap
All pressure switch tubing
is clear vinyl tubing unless
otherwise noted.
Inclined Manometer
(Differential Pressure Gauge)
Test Line
To Air Inlet
Sution Port
To Sight Glass Suction Port
White Silicone Tubing
4-Way Connector
Models 075 and 100
