Here is the sequence that allows gas to flow and ignite in a typical gas dryer.

1. Power is applied to the ignitor (igniter) and it starts to glow hot

2. The heat from the ignitor heats the flame sensor to a point sufficient to allow gas to ignite

3. The heat from the ignitor flexes a bimetal in the sensor opening the circuit to the ignitor

4. Once the circuit is open to the ignitor power is applied to the secondary coil of the coil kit

5. Current starts to flow through the secondary coil

6. As the current flows it creates an electromagnetic field opening the valve

7. Gas flows through the burner and is ignited by the still glowing ignitor

8. Heat from the now burning gas keeps the bimetal flexed in the sensor allowing the coil to remain energized keeping the gas flowing

9. Under normal conditions the control thermostat cycles off interrupting the circuit to the gas burner assembly causing the coils to loose their electromagnetic fields shutting down the gas flow