Why does car heater come on by itself?

A car heater may come on by itself due to a malfunction in the climate control system, such as a faulty thermostat or a malfunctioning control module. It could also be a result of a stuck relay, which keeps the heater running even when it's not commanded to do so. Additionally, some vehicles have automatic climate control settings that can activate the heater based on temperature sensors or driver preferences. If the issue persists, it's advisable to have the system inspected by a professional.