11
Service Manual
Table 1A Sequence of Operation
1 Service (continued)
Sequence of operation
1.
Upon a call for heat, the louver relay output will be closed initiating a block that will clear when the louver proving
switch closes. Upon resolution of all blockings, the comfort control will send the demand to the boiler control.
2.
The boiler control initiates a pre-purge and confirms that all safeties are in their correct state. During the first part of
the pre-purge, the air damper is wide open. The air damper APS is checked to be open. The proof of closure input
is checked to be closed during this time.
3.
Once the air damper APS and proof of closure are confirmed, the safeties are checked in the correct state and the
free air calibration is completed, the boiler control progresses to the second part of pre-purge. During this phase, the
dampers and fan are controlled for the ignition state. During this phase, the air damper APS must become closed.
4.
The boiler control then proceeds to trial for ignition. First, the control begins sparking, then opens the gas valve.
After sparking is complete, the control checks for the presence of a flame. If the flame is not detected, the control will
recycle or lockout on an Ignition Flame Failure. If the flame is present, the control proceeds to the flame stabilization
period. During the flame stabilization period, the flame signal must not drop below the detection threshold and
further must raise to a sufficiently high level for a stable flame. If the flame does not reach the higher threshold during
flame stabilization, the unit will recycle or lockout on Flame Loss While Running. During the flame stabilization
period and any running state thereafter, the controls will check that the proof of closure input is open.
5.
Upon successful completion of the flame stabilization period, the control will proceed to the running state, and
attempt to operate at the required modulation. At all times during operation, the damper positions and fan speed
must remain within tolerance. Further, if an O2 sensor is present and functioning properly, the unit must operate
within an expected range of O2. For operation below 10% modulation, the control will check that the air damper
APS is in the closed state.
6.
If the current call for heat is for space heating and a DHW call for heat becomes active, the control will turn on the
DHW pump relay output, then turn off the boiler pump. The control will then adjust modulation to maintain the
outlet temperature to the desired DHW outlet setpoint temperature.
7.
The boiler will modulate as needed to reach the desired set point.
8.
Once both the space heating and DHW calls for heat are satisfied, the control will turn off the gas valve and begin the
post-purge cycle. Any pumps that are running will begin their respective pump delay cycles.
9.
At the end of the post-purge cycle, the louver relay contacts will de-energize.
10.
After the fan speed falls below 3000 rpm, the air damper will be closed. The controls will check that the blower stops
running and dampers are in their expected positions. The control will check that the air damper APS reaches the
open state.
11.
After one (1) minute in standby, the O2 sensor will go into a standby state. At the end of the pump delay cycle(s),
the pump(s) will be turned off.
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