1611UDSBD-3GBEN, Pag. 31/36
UDSBD models 025-3 - 030-3
(Rotation clockwise from motor shaft end)
Figure 19
Venter
motor plate
Venter
wheel
Motor
cooling fan
Motor mounting
bracket
8 mm
The main operating quick opening gas valve is powered through the thermostat
and safety controls. The main control valve is of the diaphragm type providing
regulated gas fl ow and is preset at the factory. The gas valve requires no fi eld
maintenance except careful removal of external dirt accumulation and checking
of wiring connections. Instructions for testing pressure settings are in section 12
(see also picture 9).
21. Operating
gas valve
WARNING: The operating valve is the prime safety shutoff. All gas supply
lines must be free of dirt or scale before connecting to the unit to ensure cor-
rect sealing.
22. Combustion
air pressure
switch
The combustion air pressure switch ensures
that proper combustion airfl ow is available.
The switch senses the differential pressure
between the negative pressure in the fl ue gas
collector box and the pressure in the control
section. (For switch location, see fi gure 11b).
On startup when the heater is cold, the sensing
pressure is at the most negative level, and as
the heater and fl ue system warm up, the sens-
ing pressure becomes less negative.
If a restriction or excessive fl ue pipe length
causes the sensing pressure to be below the
allowable level, the pressure switch will shut
off the main burner. .
D A N G E R : S a f e
operation of this unit
requires proper venting
fl ow. Never bypass the
combustion air pressure
swtich or attempt to
operate the unit without
the venter operating.
If it is determined that the pressure switch needs replacing, use only the factory-
authorized replacement part that is designed for the model and size of heater
being serviced.
Figure 20
