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UBX-UBZ-UDX-UDZ-IOM (07-23) 1034344-K
CONTROLS—CONTINUED
Thermostat Options
NOTES:
• 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 030–125 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.
• Install an optional thermostat (available with the heater) or a field-supplied 24V thermostat in accordance with the
thermostat manufacturer’s instructions. Pay particular attention to the requirements regarding the location of the
thermostat.
• Ensure that if there is a heat anticipator setting on the thermostat, it is set at 0.6 amps or in accordance with the
amperage value noted on the heater wiring diagram.
• Make thermostat connections at the terminal strip on the back of the heater (see Figure 9). The strip has five
terminals: C, R, G, W1, and W2. Refer to the wiring diagram provided with the heater.
• If the heater was ordered with a multiple heater control option, one thermostat can be used to control up to five
heaters. This option includes a 40VA transformer that replaces the standard transformer in the control unit and
a relay assembly that attaches to the additional unit. Option CL31 provides for control of two heaters. If control
of additional heaters is desired (up to five total), option CL32, which is the relay assembly only, must be added
to each additional heater. The option packages are shipped separately and include complete instructions on
installation and wiring.
Circuit Board (DSI Control Module)
The heater’s ignition system is controlled by a circuit board (Direct-Spark Integrated (DSI) control module, see Figure
10) 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 UBZ
and UDZ models. To view the SSD on UBX and UDX models, the door panel requires removal. 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 10). The display’s codes are listed
and described in the Unit Troubleshooting Using DSI Control Module section.
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