What is the first step in the operation sequence for a typical gas ignition system?

In a typical gas ignition system, the first step in the operation sequence is when the thermostat closes the R-W circuit. This action signals the heating system to start. When the thermostat, which is responsible for regulating the temperature, detects that the room temperature is below the set level, it closes the circuit between the R-W terminals. This closure sends a signal to the control system, which then initiates the subsequent steps in the ignition process.

Following the closing of the R-W circuit, the control system will activate the gas valve, allowing gas to flow. This is crucial because the ignition process cannot occur until gas is available. After the gas is flowing, the ignition source (like a spark electrode or hot surface ignitor) engages, and then the furnace ignites.

Understanding this sequence is important, as it helps troubleshoot malfunctions in gas heating systems by recognizing where in the process a failure may occur. If the circuit does not close properly, the entire ignition sequence will not begin, preventing the system from heating.