AOS WPC - Tech Training 65 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
VF BOILER SERVICE MANUAL
BOILER CONTROLS (CONT)
EXTERNAL CONTROLS
Enable/Disable Control Circuit
The Enable/Disable Control Circuit is always active. This control circuit must be “closed” to
enable boiler operation. Two wires located in the junction box on the back of the boiler are
provided for this circuit. From the factory these two wires are wire nutted together.
If some form of external control is desired/required, that external control’s “dry” (no power or
load) switch contacts would be connected to this circuit through field supplied wiring run in
dedicated conduit (page 68). The external control can then enable/disable the boiler by
closing or opening its contacts. When the external control opens it’s contacts the boiler is
disabled and goes through a normal shut down sequence; the gas valve (s) close, blower (s)
run for a programmed post purge period, and the boiler goes into standby mode.
If no external control is used/connected to this circuit, the two wires must be wire nutted
together to enable boiler operation. System temperature and boiler operation is then
controlled solely by the EMC 5000 Operating Set Point working with the Controlling Probe
(page 63).
External controls, using the
provided Enable/Disable circuit,
can be used in place of the
Operating Set Point as a Primary
System Control and to provide
additional supervisory control such
as night set back, freeze
protection, and outdoor air reset
control.
MCB CIRCUIT BOARD
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