What control is used to energize the ignition control on the startup of a high-efficiency noncondensing furnace?

In a high-efficiency noncondensing furnace, the pressure switch plays a crucial role in ensuring safe and proper operation on startup. The pressure switch is designed to monitor the pressure within the combustion system and confirm that there is adequate venting for the exhaust gases.

When the furnace starts, the pressure switch is activated if it detects the correct pressure, indicating that the venting and draft are appropriate. This activation sends a signal to the ignition control, allowing it to energize and initiate the ignition sequence. This process is vital for preventing the furnace from attempting to ignite when the venting system is not functioning correctly, which could lead to dangerous conditions.

Understanding the specific functions of the other components helps clarify their roles in the system but highlights why the pressure switch is essential for the ignition process in this situation. The thermostat control, gas valve, and relay switch have important but different functions related to the overall operation and safety mechanisms of the heating system.