State SBL95 250NE A - Manual (Page 27)

27
seQuenCe of operation flow Chart
Description of this flow chart can be found in the “SeqUeNCe OF OPerATION” section found on page 26.
Thermostat calls for heat
Switch power on to unit
Blower engages Prover Switch
After 30 seconds, Ignition
Control provides power to
Spark Igniter and opens Gas
Valve
Ignition Control maintains spark for up
to 4 seconds and monitors Flame
Sensor to determine if Burner is lit
Does Burner
light?
Ignition Control changes Blower from
low speed to high speed after 5 seconds
Ignition Control monitors
flame signal
Thermostat is satisfied
Blower – off; Blower Prover – opens
Ignition Control – off; Gas Valve – closes
Wait 15 minutes.
Blower runs at
low speed
Is this the third loss
of flame signal?
Is this the third
ignition trial?
Loss of flame signal?
YES
YES
NO
NO
Gas Valve – off
Gas Valve – off
NO
NO
YES
YES
UGB sends PWM signal to Blower to
start the blower at high purge speed
20 seconds later blower
runs at low igniƟon speed
figure 24.