What does the pressure switch do in a gas furnace?

The pressure switch in a gas furnace plays a critical role in safety and operational efficiency by ensuring that there is sufficient airflow before the furnace's burners are ignited. This component detects whether the exhaust gases are being expelled properly through the venting system, which is essential to prevent the accumulation of dangerous gases like carbon monoxide within the furnace.

When the furnace begins to operate, the pressure switch verifies that a proper airflow is present, indicating that the venting system is clear and functional. If adequate airflow is not detected, the pressure switch will not allow the ignition system to activate, thereby preventing potential hazards associated with insufficient venting. This crucial safety feature effectively protects both the equipment and the occupants of the space it heats.