A customer complains that her house is too warm and the technician finds the gas valve stuck open. What action should the technician take?

The most appropriate action in this scenario is to replace the gas valve. When the gas valve is stuck open, it allows an uncontrolled flow of gas into the system, leading to excessive heating and potentially hazardous conditions, such as a risk of overheating or even fire.

In this situation, simply adjusting the thermostat settings would not address the underlying issue of the gas valve malfunctioning. Cleaning the furnace filters, while beneficial for overall efficiency and air quality, would not solve the immediate problem of the gas valve being stuck, as it is more related to airflow than the gas control mechanism. Checking the blower motor could be useful for resolving airflow issues, but it does not relate to the root cause of the excessive heat caused by the open gas valve. Therefore, replacing the gas valve is the necessary step to restore proper function and safety to the heating system.