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UBX-UBZ-UDX-UDZ-IOM (07-23) 1034344-K
High Temperature Limit Control
⚠ WARNING ⚠
The automatic-reset high temperature limit control will continue to shut down the heater until the
cause is corrected. Never bypass this control as hazardous conditions could result.
All units are equipped with a temperature-activated, automatic-reset high temperature limit control (see Figure 11
for location). The control is factory-set and is non-adjustable. If the setpoint is reached, the control interrupts the
electric supply to the combination gas valve. This safety device provides protection in the case of motor failure or
lack of airflow due to a restriction at the inlet or outlet.
Flame Rollout Switch (UDX and UDZ Model Unit Sizes 030–125)
⚠ 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 030–125 of UDX and UDZ models are equipped with a temperature-activated, manually-reset flame rollout
switch (see Figure 11 for location). The switch 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.
Interlock Door Switch (UBZ and UDZ Models)
All UBZ and UDZ model units are equipped with an interlock door switch (see Figure 11 for location) that prevents
the heater from operating when the service door panel is open. The service panel is equipped with a pliable gasket
that fully seals the door to provide added protection to prevent building air from entering the combustion zone of
the heater.
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 11 for location) 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
The fan motor 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 nameplate to
verify its horsepower.
Venter Motor
The venter motor (see Figure 11 for location) is assembled to the venter wheel and operates to provide combustion
airflow. Operation is controlled by the circuit board (see Figure 10). Refer to the Circuit Board (DSI Control Module)
section for details.
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