Burner Operation
When the main burner is lit, a flame rectification circuit is completed between the flame sensor (igniter on local sense
systems or flame rod on remote sense systems) and the main burner (burner ground). The S8910U flame sensing
circuit detects the flame current and holds open the gas control. The main flame is monitored continuously during the
call for heat.
Safety Shutdown
One Trial Selection Tabs (A and C)
If flame is not sensed by the end of the timed trial for ignition, the gas control closes and the module locks out. It must
be manually reset by removing power or setting the thermostat below the room temperature for at least 30 seconds.
If the burner lights and flame is proved but goes out during the run cycle, the gas control closes and the module
initiates a warmup period followed by one trial for ignition. If flame is not established, the gas control closes and the
module locks out, requiring manual reset.
Three Trial Selection Tabs (B and D)
If flame is not sensed by the end of the first timed trial for ignition, the gas control closes and the module initiates a
second 96 seconds between trial purge cycle, followed by igniter warmup and a second trial for ignition. If flame is
not established, the between trial purge, warmup, trial for ignition cycle is repeated a third time. If flame is still not
established following the third trial, the gas control closes and the module locks out. It must be manually reset by
removing power or setting the thermostat below the room temperature for at least 30 seconds.
If the burner goes out during the run cycle, the gas control closes and the module checks for the number of ignition
trials performed during the current call for heat. If the number is less than three, the module initiates a between trial
purge, warmup and trial for ignition. After the third trial during a single call for heat, the module locks out. The module
must be manually reset following the lockout.
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