16 Servicing should only be performed by a Qualied Service Technician
SeQuence of operaTion – floW charTThermostat calls for heat
Switch power on to unit
Blower engages Prover Switch
Aer 30 seconds, Ignion
Control provides power to
Spark Igniter and opens Gas
Valve
Ignion Control maintains spark for up
to 4 seconds and monitors Flame
Sensor to determine if Burner is lit
Does Burner
light?
Ignion Control changes Blower from
low speed to high speed aer 5 seconds
Ignion Control monitors
flame signal
Thermostat is sasfied
Blower – off; Blower Prover – opens
Ignion 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
ignion trial?
Loss of flame signal?
YES
YES
NO
NO
GasValve–off
GasValve–off
NO
NO
YES
YES
UGB sends PWM signal to Blower to
start the blower at high purge speed
20 seconds later blower