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VHX SERIES STEAMER - ELECTRICAL OPERATION
F24700 (October 2001) Page 42 of 68
Auxiliary Low Level Cut-Off
This control serves as a safety backup to the main
water level control (WLC) board to meet CSD-1
code requirements. The operation of the auxiliary
control is identical to the low level cut-off (LLCO)
function of the main WLC board but performs a
single function: 1) Provide auxiliary low level cut-off
protection to shut off the heat source in case the
water level drops below the low level cut-off (LLCO)
probe. A single LLCO probe, identical to the LLCO
probe on the main WLC board, is connected to the
auxiliary control.
The auxiliary water level control (WLC) has input
voltage (120VAC) across terminals 11 and 12 which
powers the primary side of the transformer. On one
side of the transformer secondary, power is
provided to the control by a series path through
chassis ground (terminal 10). The other side of the
transformer secondary (12VAC) is attached to the
control that directs power to the other side of the
internal relay (LLCO). As water enters the boiler, it
becomes part of the auxiliary water level control’s
circuit. When the water level in the boiler reaches
the LLCO probe, the circuit is completed.
When the main power switch is turned ON, power is
supplied to the auxiliary WLC board but no
switching occurs. Also, the low water level indicator
light (amber) on the boiler base control panel comes
on.
When the water level reaches the low level cut-off
(LLCO) probe, the LLCO relay is energized (LLCO-2
close) and the LLCO LED lights up. The LLCO relay
will remain energized and its LED will stay lit until
the water level in the boiler drops below the LLCO
probe.
When the boiler stops filling, press the manual reset
switch on the boiler base control panel. This turns
off the low water light, energizes the combustion
blower and allows the ignition cycle to begin.