Both direct-spark and hot-surface ignition systems are dependent upon a solid-state ignition control module. This module sends and receives messages to/from other components within the ignition system. There is one main difference in operation between the two systems. In the direct-spark system, a spark ignites the main burner; in the hot-surface system, there is no spark. The operational sequence of both hot-surface and direct-spark systems are listed below.
Operation sequence of the hot-surface ignition system:
- When there is a need for heat, the thermostat contacts close, sending a signal to the control module. The control module is a self-diagnostic device. It immediately starts to perform a self-check. If the module senses a problem externally or internally, it responds by flashing an indicator light. The control module will check for closed limit contacts on the pressure switch.
- The induced draft blower will then start and purge the system for 30 seconds.
- After the pre-purge, the silicon carbide ignitor becomes energized. This occurs for about 17 seconds before the gas valve opens.
- When the gas valve is energized, gas flows to the burner and the heated ignitor. The gas is ignited.
- During normal operation, the ignitor becomes de-energized approximately 4 seconds after the gas valve is energized.
- Through the flame sensor, the control module must detect main burner operation within 4 to 7 seconds. If it does not, the gas valve will become de-energized. After burner flames have been sensed, the fan blower motor is energized. This is accomplished through a time delay within the control module.
- When the thermostat becomes satisfied, the gas valve is de-energized, along with the inducer blower. The adjustable delay-to-fan-off sequence begins to de-energize the fan blower.