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8
Operating information
Sequence of operation
OPERATION
1. Upon a call for heat, the gas pressure switch(es) must be closed.
2. Once the gas pressure switch(es) are closed, the control turns
on the appropriate pumps (system and boiler pumps for space
heating, DHW pump for DHW). The fl ow switch and/or LWCO
must close.
3. The air pressure switch and blocked drain switch must close.
4. The control starts the prepurge cycle by initiating the blower.
5. The control starts the trial for ignition by fi ring the spark
electrode and opening the gas valve.
6. If fl ame is not detected after the sparking ends, the control will
perform a postpurge, then start another prepurge cycle and try
to light the burner again. On the 501 and larger models, the control
will lock out if this second attempt also fails. On the 400 model,
the control will perform a total of 4 attempts before locking out.
7. If fl ame is detected, it holds the fi ring rate steady for a few
seconds to let the fl ame stabilize, then it begins to modulate the
fi ring rate based on a set point or some other command (such
as a 0-10V BMS signal).
Outdoor Knight XL Installation & Operation Manual
(continued)
DISPLAY
43
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