• 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 six 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.
Main Operating Gas Valve
⚠ WARNING ⚠
The main operating 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 main operating gas valve (see Figure 25 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 25 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 18.
Table 18. Pressure Switch Settings
Unit
Size
Negative Pressure (IN WC)
Label
Color
Switch
PN
Startup Cold Equilibrium Hot Setpoint OFF Setpoint ON
130 3.50 3.00 2.40 2.65 White 1013436
180 3.20 2.50 2.30 2.45 Blue 221228
260 3.50 3.10 2.40 2.65 White 1013436
310 3.30 2.80 2.40 2.65 White 1013436
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 25
for location). The control is factory-set and is non-adjustable. If the setpoint is reached, the control interrupts the
electric supply to the 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.
35
I-UEZ (04-21) 1034347-0
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