Ignition System Furnace Troubleshooting

Ignition System Furnace Troubleshooting ChicagoBoth  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:

  1. 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.
  2. The induced draft blower will then start and purge the system for 30 seconds.
  3. After the pre-purge, the silicon carbide ignitor becomes energized. This occurs for about 17 seconds before the gas valve opens.
  4. When the gas valve is energized, gas flows to the burner and the heated ignitor. The gas is ignited.
  5. During normal operation, the ignitor becomes de-energized approximately 4 seconds after the gas valve is energized.
  6. 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.
  7. 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.

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