A.O. Smith VF VB 1000 Service Handbook page 64

BOILER CONTROLS (CONT)
Controlling Probe
The Operating Set Point on the VF boiler's EMC 5000 control system reacts to temperature
sensed by the Controlling Probe.
The EMC 5000 control system can be configured to use either the Inlet probe or the remote
Tank/Loop probe as the "Controlling Probe." VF boilers are designed to use the remote
Tank/Loop probe as the Controlling Probe. Review the installation and configuration
information on page 62.
INTERNAL TEMPERATURE CONTROLS
Operating Set Point - User Setting "Oper Setpnt"
The Operating Set Point is always active and is a Primary System Control (page 62)
when there is no external primary system control in use. The Operating Set Point has a
range of 70°F to 190°F for VW models and 70°F to 220°F for VB models (page 70). The
Operating Set Point is a local EMC 5000 User Setting that can be adjusted through the UIM
(page 8). See the dead-band operational note on page 64.
The Operating Set Point reacts to temperature sensed by the Controlling Probe. When
the temperature sensed at the Controlling Probe drops below the Operating Set Point minus
the Stage 1 Differential AND the Enable/Disable circuit (page 65) is closed, a call for heat is
activated.
When an external control is used as the Primary System Control set the Operating Set
Point at least 20°F higher than the Primary System Control setting to ensure reliable system
temperature control and avoid conflict and short cycling between the two set points.
Stage 1 Differential Setting - User Setting "Stage1 Diff"
This is a "local" EMC 5000 User Setting that can be adjusted through the UIM (page 8).
When the temperature sensed at the Controlling Probe drops below the Operating Set Point
minus the Stage 1 Differential setting a call for heat is activated. IE: with the settings shown
in the screen shot below the call for heat would not be activated until the temperature
sensed at the Controlling Probe dropped to 157° F (160 - 3 = 157). The call for heat is
deactivated when the temperature sensed by the Controlling Probe rises to the Operating
Set Point.
Stage 1 Differential setting has a range of 1°F to 50°F. The higher the setting the wider the
system temperature swing will be. The default setting is 3°F which is a good initial setting.
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VF BOILER SERVICE MANUAL
Servicing should only be performed by a Qualified Service Agent
63 of 72 Ashland City, TN © 2007