What causes the fan to run non stop?

A fan may run non-stop due to a faulty thermostat that fails to detect temperature changes, causing the fan to remain on continuously. Additionally, issues with the fan's control board or wiring can lead to a malfunction, keeping the fan operational. In some cases, the fan is designed to run continuously for improved air circulation or to maintain consistent temperatures. Lastly, a clogged air filter can restrict airflow, prompting the fan to work harder and potentially run longer.