Boiler Control Instruction & Operation Manual
Page
13
of
68
Product Features
Multiple Boiler Control Sequencer (continued)
Improved Availability
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The following features help improve the heat availability:
Backup Header Sensor
In the event of a header sensor failure the lead boil
er’s supply sensor is used by the Sequence Master
to control firing rate. This feature allows continued coordinated sequencer control even after a header
sensor failure.
Slave Boiler Rate Adjustment
Each slave boiler continues to monitor supply, return and flue gas temperatures and modifies the
Sequence Master
’s firing rate demand to help avoid individual boiler faults, minimize boiler cycling and
provide heat to the building efficiently.
Slave Boiler Status Monitoring
The Sequence Master monitors slave boiler lockout status and automatically skips over disabled boilers
when starting a new slave boiler.
“Stand Alone” Operation Upon Master Failure
Individual boilers are configured to continue to operate in the event the Sequence Master Control is
powered down, disabled or Boiler-to-boiler communication is lost.
The following are design
considerations for backup
“Stand Alone” operation;
Enable/Disable
Upon loss of the Sequence Master each boiler will automatically begin local control. This
means it will operate only if it has a call for heat. For this reason slave boilers should have their
“External Enable/Disable” J8 terminal 1 to 3 jumpered. In the event of loss of Sequence Master
the slave boiler will have demand to run.
Modulation
Once running the Slave boiler will use the selected central heat modulation sensor and setpoint
to produce heat for the building. Optionally, slave boilers may have a separate header sensor
wired and select the
“Central Heat Modulation Sensor” parameter as Header Sensor”. This will
allow continued header water temperature control.
Pumping
Consideration must be given to how the system pump is powered. If the Sequence Master
enabled boiler is powered down, how will the system pump be operated? It may be required to
wire the system pump to multiple boilers.
Once the Sequence Master is restored to operation the individual boilers automatically resume their
position as sequencer slaves.
