Schwank SEB(U) User Manual

Page 21

SP-MSEB-BX-10A

SEB Manual

RD: JUNE 2004

RL: 10

Page 17

16. SEQUENCE OF OPERATION / FLAME RECOVERY/ SAFETY LOCKOUT

Start up - Heat Mode

When the thermostat is set above the ambi-
ent 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 prepurge*, if selected. Fol-
lowing the pre-purge, the gas valve is ener-
gized and sparks commence until flame is
detected or the Trial For Ignition (TFI) pe-
riod 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
satisfied 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
period, the gas valve is de-energized and the
control starts the inter-purge sequence be-
fore another ignition attempt. After inter-
purge, the control will attempt two addi-
tional ignition 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 com-
pleted 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 estab-
lished, 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