Power-Up
Upon applying power (120 volts), the control will reset, perform a self-check routine, monitor the flame sense input to verify no flame is present and enter the thermostat scan state.
Call for Heat
When a call for heat is received from the thermostat supplying 120 volts to the TH terminal, the control will perform a self-check routine, the safety timing sequence and flame check. After an optional pre-purge period, the hot surface ignitor is energized for a heat-up period, followed by the gas valve for the trial for ignition (TFI) period. If flame is detected during purge, the gas valve will remain de-energized.
Ignition
When a valid flame is detected during the TFI period, the ignitor is de-activated and the gas valve remains energized. The thermostat and main burner flame are constantly monitored to assure that the system operates properly. The control will continuously monitor the flame during the heating period. (If flame is lost, the gas valve will be shut off within 0.8 seconds.) When the thermostat is satisfied and the demand for heat ends, the gas valve is de-energized imme- diately.
System Failure During Trial-for-Ignition Period
The robust design of our gas ignition controls is demonstrated by their ability to respond to flame failures in a safe manner and provide re-ignition options for the appliance designer
Flame Failure During Trial-for-Ignition Period
SINGLE TRIAL MODEL
Should the main burner fail to light or the flame is not detected during the TFI, the control will lockout. The gas valve will be turned off immediately. With the 1 hour reset option, if the thermostat is still calling for heat, the control will automatically reset and attempt a new TFI after one hour.
MULTI TRIAL MODEL
Should the main burner fail to light or the flame is not detected during the first TFI, the gas valve is de-energized and the control performs an optional inter-purge delay before attempting another TFI. The control will attempt 2 additional TFIs before locking out. In lockout, the gas valve will be turned off immediately. With the 1 hour reset option, if the thermostat is still calling for heat, the control will automatically reset and attempt a new TFI after one hour.
Flame Failure of Established Flam
RE-IGNITION
If the established flame signal is lost while the burner is operating, the control will respond within 0.8 seconds and de-energize the gas valve. The control performs an optional inter-purge delay before attempting a new TFI. If the burner does not re-light, the control will lockout as previously described in the 'Failure to Light - Lockout' section. Multi-try models will make 2 more attempts to light the burner. If flame is re-established, normal operation resumes.
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 mode. The control will not open the gas valve unless there is intervention by the user. See Lockout Recovery.
Lockout Recovery
Recovery from lockout requires a manual reset by either resetting the thermostat or by removing the 120 volts for a period of 5 seconds.
