UTICA BOILERS UB90125 Installation, Operation And Maintanance Manual page 42

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.
The following steps and diagram indicate the
location of the connection points required to
measure the offset pressure using an Inclined
Manometer or a Differential Pressure Gauge.
Only one device is required to measure the
offset pressure.
1. Turn off service switch, or lower thermostat
setting.
2. Remove vinyl caps from Tee.
3. Install testing lines as shown to Inclined Ma-
nometer 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 thermostat
to call for heat.
5. If manometer readings do not correspond
to the chart at right, check for possible
causes:
• Blockage or moisture in suction lines to
switch.
• Blockage or moisture in orifice installed
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 pressure
switch setpoint.
• Gas valve out of adjustment.
6. When the pressure reading corresponds to
the chart at right and the pressure switch is
operating properly, remove the testing lines
and reinstall the vinyl caps to the Tee and
3-way connector.
troUBlesHootiNg
dIFFEREntIal aIR pREssuRE sWItcH cHEcK
Running Without
(Approximate mini-
mum vent lengths)
Locations of the connection points required to check
the differential air pressure.
Boiler status Differential Pressure switch
Not Running
1.00" for Model 125
1.50" for Model 150
Blockage
1.50" for Model 175
2.00" for Model 200
Running With Greater Than or Equal
Blockage To Setpoints
42
3.5"
0"
0.5"
3.5"
0.5"
3.5"
0.5"
contacts
Closed
Open
Closed
Closed
Open
Closed