Effective: August 2015
2
F-35-63
SEQUENCE OF OPERATION / FLAME
RECOVERY / SAFETY LOCKOUT
Start Up - Heat Mode
When a call for heat is received from the thermostat supplying 24
VAC to TH/W, the control will reset, perform a self-check routine,
flash the diagnostic LED and begin a pre-purge delay. Following
the pre-purge period, the pilot gas valve is energized and
sparking commences for the Trial For Ignition (TFI) period. The
main gas valve remains de-energized until the pilot flame is
detected.
When the pilot flame is detected during TFI, the sparking process
is terminated and the main gas valve is energized. The
thermostat and pilot burner flame are constantly monitored to
assure proper system operation. When the thermostat is satisfied
and the demand for heat ends, the pilot and main valves are
immediately de-energized.
Failure to Light - Lockout
SINGLE TRIAL MODEL
Should the pilot burner fail to light or the pilot flame is not
detected during the TFI period, the pilot valve will de-energize
and the control will go into lockout. The LED will indicate the fault
code for ignition lockout.
MULTI TRIAL MODEL
Should the pilot burner fail to light or the pilot flame is not
detected during the first TFI period, the pilot valve will de-
energize. The control then goes through an inter-purge delay
before an additional ignition attempt. The control attempts two
additional ignition trials before de-energizing the pilot valve and
entering lockout.The LED will indicate the fault code for ignition
lockout.
FLAME FAILURE-RE-IGNITION MODE
If the established pilot flame signal is lost while the burner is
operating, the control will respond within 0.8 seconds by de-
energizing the main gas valve and energizing the H.V. spark for
the TFI period in an attempt to relight the pilot burner. If the pilot
burner does not light within the TFI, the pilot gas valve will
immediately de-energize and single try models will enter lockout.
On multi-try models, a new TFI sequence will begin after an
inter-purge delay. Multi-try models perform two additional
attempts to light the burner before de-energizing the gas valves
and entering lockout. If the pilot burner relights, normal
operation resumes.
FLAME FAILURE-RECYCLE MODE
With the “Recycle after Loss of Flame" option, upon loss of pilot
flame, the pilot and main gas valves are de-energized and the
control proceeds to inter-purge before attempting to relight the
pilot flame. Multi-try models permit three tries for ignition
including inter-purges. If the pilot burner relights, normal
operation resumes. If the pilot burner does not relight, the
control will enter lockout.
Lockout Recovery
Recovery from lockout requires a manual reset by either resetting
the thermostat, or removing 24 VAC for a period of 5 seconds.
On models with automatic reset, if the thermostat is still calling
for heat after one hour, then the control will automatically reset
and attempt to ignite the burner.
