Boiler Controls Information - A.O. Smith VF VB 1000 Service Handbook

BOILER CONTROLS
Boiler controls that are improperly installed or set up can cause serious operational and service
related problems such as short cycling. This section provides information for how various
controls can work together or independently to provide proper system and boiler control.
Two conditions must be met for the VF boiler to start a heating cycle:
1. The Operating Set Point (page 8 and 63) which responds to temperature sensed by the
Controlling Probe (page 63) must be "calling for heat." The Operating Set Point (page
63) is always active and must be calling for heat or the boiler will not fire.
The EMC 5000 control system, using it's own Operating Set Point and a remote Tank/
Loop probe, can provide reliable system temperature control as a Primary System
Control (page 62) independently or work with an external supervisory control utilizing
the Enable/Disable circuit.
2. The Enable/Disable circuit (page 65) must be closed. Two wires are provided in the
wiring junction box on the back of the boiler for this circuit. The Enable/Disable circuit is
provided to allow the VF boiler to be started or stopped by different forms of external
supervisory controls (page 65) including: Aquastats, Boiler Sequencing Controllers, and
EMS - Energy Management Systems.
The Enable/Disable circuit is always active, if an external control is not using this circuit
for supervisory control, the two Enable/Disable wires in the junction box must be wire
nutted together or the boiler will not fire. See the illustration below.
The "Operating Set Point" is an
internal User Setting adjusted at
the boiler. It may be used as a
stand alone "Primary System
Control."
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.
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VF BOILER SERVICE MANUAL
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