An intermittent pilot ignition module is a solid-state ignition device used to automatically light a pilot burner and simultaneously energize (operate) the main gas valve of the heating system when the room thermostat calls for heat (see Figure 5-65). Figure 5-66 illustrates the wiring connections between an intermittent pilot module, the dualvalve
combination valve, and the combined pilot burner and igniter sensor unit.
The operating sequence for a gas burner operated by an intermittent pilot ignition control is as follows:
1. Room thermostat calls for heat, and the intermittent pilot ignition module simultaneously opens the pilot valve and supplies a continuous spark to the electrode in the pilot burner.
2. Pilot burner gas ignites and produces a flame.
3. Pilot flame sensor detects the pilot flame and signals the intermittent pilot ignition control to discontinue the spark and energize (open) the main gas valve.
The main gas valve will not be energized until the flame sensor detects the presence of the pilot flame. As long as the main gas valve remains closed, no gas from the supply line can flow through the burners. Should a loss of flame occur, the main gas valve closes and the spark recurs within 0.5 second.
4. Gas from the gas supply line flows through the now-open main gas valve to the burners and ignites. This is the burn or on cycle. When the heat has reached the level required by the thermostat setting, the main gas closes and the burner or burners shut down. This is the off cycle in an intermittent pilot ignition control system.
Some Useful Definitions
• Run—The period during which the main gas valve remains energized and the spark is turned off after the successful
ignition.
• Trial for ignition—The period during which the pilot valve and spark are activated, attempting to ignite gas at the main gas burner.
• Flameout—The loss of proven flame.
• Proven flame—A pilot flame detected by a flame sensory device.
• On cycle—Period of time during which the main gas valve is open and the burners are operating.
• Off cycle—Period of time during which the main gas valve is closed and the burners are not operating.
If the pilot flame is extinguished, even though the room thermostat is still calling for heat, the intermittent pilot ignition control immediately deenergizes the main gas valve, causing it to close its open supply port and stop the flow of gas to the burners. A spark at the pilot burner electrode will recur within 0.8 second.
As soon as the pilot flame is reignited and detected by the pilot flame sensor, the main gas valve is energized, the valve port is opened, and the spark is extinguished. The intermittent pilot ignition control then deenergizes the pilot gas and main burner gas valve when the thermostat stops calling for heat.
