What is an immediate indicator of a properly functioning gas valve in a furnace system?

A properly functioning gas valve in a furnace system should open in response to a signal from the thermostat when there is a call for heat. This action indicates that the valve is operating correctly because it is allowing gas to flow to the burner assembly, which is essential for igniting the fuel and generating heat.

When the thermostat reaches the set temperature, it sends a signal to the gas valve to either open or close. If the valve opens as expected, it shows that the system components are communicating effectively and that the valve is responsive to the thermostat's commands, which directly influences the heating function of the furnace.

Other indicators, like being able to manipulate the valve by hand or maintaining steady pressure, may not directly verify its operational status. Similarly, the absence of sounds during operation does not definitively indicate that the valve is functioning properly, as some normal operational sounds can be expected during the ignition and running cycles. Thus, the most immediate and relevant indicator of a gas valve's proper function is its ability to open upon demand from the thermostat.