Schwank IT(U) - Manual (Page 25)

GP-MSEM-BX-06A
SEM(U) / IT(U) Manual
RD: Aug 2006
RL: 06A
KH
17. SEQUENCE OF OPERATION / FLAME RECOVERY/ SAFETY LOCKOUT
Start up - Heat Mode
When the thermostat is set above the ambient
temperature, 120 VAC is supplied to the L1
terminal. When this occurs the control
will power up and perform a self-check rou-
tine and begin a pre-purge*, if selected. Fol-
lowing the pre-purge, the gas valve is ener-
gized and sparks commence until flame is de-
tected or the Trial For Ignition (TFI) period
expires.
When flame is detected, the spark is shut off
and the gas valve remains energized. The
thermostat and burner flame are constantly
monitored to ensure that the system is func-
tioning properly. When the thermostat is sat-
isfied and the demand for heat ends, the gas
valve is de-energized immediately and the
flame is extinguished.
Flame Failure During TFI Period
Should the burner fail to light or flame is not
detected during the first trial for ignition pe-
riod, the gas valve is de-energized and the
control starts the inter-purge sequence before
another ignition attempt. After inter-purge,
the control will attempt two additional igni-
tion trials. If these attempts are unsuccessful
the control will go into lockout mode.
Flame Failure of Established Flame
Re -Ignition
If the established flame signal is lost while
the burner is operating, the control responds
and begins sparking within 0.8 seconds. The
spark will be energized for the duration of the
trial-for-ignition period in an attempt to re-
light the burner. If flame is re-established,
normal operation resumes.
If the Burner does not light after the first at-
tempt, the inter-purge sequence is completed
between attempts to re-light the burner. If the
burner fails to light after the
third try, the control will de-energize the gas
valve and go into lockout mode. See
Lockout Recovery
Lockout Mode (On-Board Safety System)
After single or multiple attempts to light the
burner have failed or flame is not established,
the control automatically enters lockout The
control will not open the gas valve unless
there is intervention by the user. See Lockout
Recovery.
Lockout Recovery
For lockout recovery, reset the thermostat
below ambient temperature or remove the
120 VAC power supply for 5 seconds
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