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UEZ-IOM (07-23) 1034347-I
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.
• For all availaible thermostat and thermostat accessory options, contact 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 25). 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.
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 the unit to ensure positive closure.
The combination gas valve (see Figure 27 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.
Pressure Switch
⚠ DANGER ⚠
Safe operation of this unit requires proper venting flow. NEVER bypass the pressure switch or
attempt to operate the unit without the venter running and the proper flow in the vent system.
Hazardous conditions could result.
• The pressure (combustion air proving) switch (see Figure 27 for location) is a pressure-sensitive switch that
monitors air pressure to ensure that proper combustion airflow is available.
• The pressure switch senses the differential pressure between the negative pressure in the venter housing and
the pressure in the cabinet.
• At startup when the heater is cold, the sensing pressure is at the most negative level, and as the heater and vent
system warm up, the sensing pressure becomes less negative. After the system has reached equilibrium (about
20 minutes), the sensing pressure levels off.
• If a restriction or excessive vent length/turns cause the sensing pressure to be outside the pressure switch setpoint,
the switch will function to shut off the main burner. The main burner will remain off until the system has cooled
and/or the flue system resistance is reduced.
• Pressure switch settings are listed in Table 19.
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