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Installation & Operation Manual
55
11 Operating information (continued)
OPERATION DISPLAY
1. Upon a call for heat, the control turns on the appropriate pumps
(system and boiler pumps for space heating call; DHW pump for
DHW call).
BLR: Standby
OUT: 123.8F(129)
2. The control connects 120 vac to the blower. The blower does
not run at this time.
• If the unit is equipped with a flow switch or low water cutoff, it
must close before the control powers up the blower.
• If the unit is equipped with a manual reset high limit it must be
closed before the control powers up the blower.
• If the unit is equipped with a solenoid valve and/or a vent
valve, they will be energized along with the blower.
• If the unit is equipped with a gas pressure switch, it must close
at this time.
• If there is an auxiliary device connected to the unit, the unit will
then provide 24 vac to its enable relay. If the auxiliary device
has a proving switch, it must close before the sequence
continues.
BLR: Standby
OUT: 123.8F(129)
3. The control then starts a 10 second prepurge cycle.
BLR: PREPURGE
OUT: 123.9F(129)
4. Once the prepurge cycle is complete, and the blocked drain
and auto-reset high limit are closed, the control starts the 5
second trial for ignition by sending spark voltage to the spark
electrode and opening the gas valve.
BLR: IGNITION
OUT: 123.9F(129)
5. If the control does not detect flame by the end of the trial for
ignition, the control performs a 10 second postpurge, another
prepurge and tries to light the burner again. If the burner does
not light after 4 trials, the control locks out for 1 hour and then
tries another set of 4 trials.
BLR: POSTPURGE, PREPURGE
OUT: 123.9F(129)
6. If the control detects a flame before the trial for ignition ends, it
begins to modulate the burner in order to maintain the set point.
If the boiler lights due to a space heating call for heat, and the
ramp delay function is active (default is active), the modulation
will be held to a series of increasing limits after the burner has
lit.
BLR: SH 20% RATE
OUT: 124.8F(129)
7. If the space heating call for heat is active, and the DHW thermostat
closes, the control will turn on the DHW pump, wait 2 seconds, and
then turn off the boiler pump. This will divert the hot water away
from the heating zone(s) and send it to the DHW tank instead. The
control will then modulate to maintain the outlet temperature to the
DHW boiler set point.
BLR: DHW 85% RATE
OUT: 177.8(180)
Sequence of operation