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BOILER CONTROL: INTERNAL WIRING & OPERATION
Period
A heat demand has no influence in the Safety On/Off period.
The Safety On/Off step will continue even if the demand
Safety
has ended.
On/Off
This step very quickly opens and closes the gas valve relays and determines if the control is operating correctly. The CH pump is
turned off during this test.
A heat demand has no influence in the Pre-Ignition period.
Pre-Ignition
Once the internal check is complete, the control begins a Pre-Ignition sequence. The igniter is energized while the gas valve
remains off. If a flame is detected at the end of the pre-ignition period a lockout will occur.
A heat demand has no influence in the Ignition period.
Ignition
The igniter remains energized for the first 4 seconds of the Ignition period. For the final 2 seconds of the Ignition period, the igniter
is turned off and the control checks for a flame signal through both the ignition electrode and the flame sensor. If no flame signal is
present at the end of the Ignition period, the control initiates a post-purge and then begins the ignition cycle again. If there are
three consecutive ignition failures, the control will post purge and lockout.
A heat demand must be present for the control to stay in
this period.
Burner On
Once the flame signal is established, the burner will run until the demand is satisfied, the setpoint is exceeded, or a blocking error
occurs. The maximum run period for the burner is 24 hours. If the boiler runs continuously for 24 hours, the control will override
the demand and turn off the burner. After this a restart will occur and the burner will continue to run.
After the Post Purge period begins, a heat demand will be
ignored until after this period.
Post Purge 1
During post purge 1, the control monitors the flame signal to be sure that the flame has extinguished. If a flame is detected after
the maximum 10 second time period, a control lockout will occur.
During this period a heat demand has no effect on operation.
Post Purge 2
During this period, the combustion air fan runs at high speed to purge combustion gases from the heat exchanger. The fan post
purge period is 30 seconds.
No heat demand is present.
Pump Purge
The operation of the circulators and the boiler depend on the pump mode and the heat demand status.
32
Demand Status
User Interface Display
The following displays occur on ignition failure only.
The following screen is displayed when the demand has ended.
The following screen will be displayed if the supply temperature
exceeds the target setpoint.
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