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UBXC-UDXC-IOM (01-24) 1042980-0
Flame Rollout Switch (Model UDXC, Unit Sizes 30–125)
⚠ DANGER ⚠
If the manual-reset flame rollout switch activates, identify and correct the cause before resetting
the switch. Never bypass the flame rollout switch; hazardous conditions could result.
Unit sizes 30–125 of model UDXC are equipped with a temperature-activated, manually-reset flame rollout switch
(see Figure 20). The switch, located behind the top burner body support, is factory-set and is non-adjustable. If the
setpoint is reached, the switch interrupts the electric supply to the gas valve. If the flame rollout switch activates,
identify and correct the cause before resetting the switch.
Combination Gas Valve
⚠ WARNING ⚠
The combination gas valve is the prime safety shutoff. All gas supply lines must be free of dirt or
scale before connecting them to the unit to ensure positive closure.
The combination gas valve (see Figure 20) is powered by the 24V control circuit through the thermostat and safety
controls. The diaphragm-type valve is pre-set at the factory and provides regulated gas flow.
Fan Motor (Model UDXC)
The fan motor (see Figure 20) is equipped with automatic-reset thermal overload protection. If the motor does not
run, the cause may be due to improper current. Ensure that the correct voltage is available at the motor.
NOTE: If the unit is equipped with an optional, totally-enclosed motor or optional voltage, the
motor’s horsepower may be greater than the standard motor. Refer to the motor’s nameplate to
verify its horsepower.
Thermostat
NOTE: IMPORTANT: all units MUST be operated by a 24V thermostat. Never use a line voltage
disconnect switch as a means of operating the heater. The operation of unit sizes 30–125 by means
other than by a 24V thermostat may result in the flame rollout switch tripping. For all availaible
thermostat and thermostat accessory options, contact an authorized Factory Distributor.
The unit may be controlled by a thermostat—either an optional thermostat (refer to Table 7) or a field-supplied 24V
thermostat that must be field-installed in accordance with the thermostat manufacturer’s instructions. Pay particular
attention to the requirements regarding the location of the thermostat. In accordance with the wiring diagram provided
with the unit, connect the thermostat at the 24V control wiring terminal strip on the back of the unit (refer to Control
Connections section).
Circuit Board (DSI Control Module)
The heater’s ignition system is controlled by a circuit board (see Figure 20), a Direct-Spark Integrated (DSI) control
module (see Figure 18), that monitors the safety devices and controls the operation of the fan and venter motors and
the combination gas valve between heat cycles. The module’s Seven-Segment Display (SSD) is visible through a
viewport on the access door panel. In addition, there is a status LED on the bottom of the heater. Its status indications
are off (heater is not powered or control board fault), steady on (heater is on with no faults), or flashing (heater
is on with fault(s)). Additional status indications appear on the display at the bottom of the control module (labeled
as DSP1, see Figure 18). The display’s codes are listed and described in the Unit Troubleshooting Using DSI
Control Module section.
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