resideo S8910U3000 Manuel D'installation page 15

Module operation is in three phases—prepurge/igniter
warmup, trial for ignition and burner operation. The
S8910U provides one or three trials for ignition,
depending on the DIP switch configuration. Fig. 6 shows
the normal operating sequence.
Purge/Prepurge
When the S8910U is used in a fan-assisted combustion
system, the combustion air blower starts on a call for heat
from the thermostat. On proof of airflow, the air proving
switch closes and energizes the S8910U. When the
S8910U is used in an atmospheric system, the call for
heat energizes the module.
In either case, the S8910U first initiates a 32-second delay
to allow system prepurge.
Igniter Warmup
After prepurge, the S8910U energizes the igniter to start
the igniter warmup. The module energizes the hot surface
igniter for the selected warmup period; the gas control is
closed during this period.
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S8910U3000
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