Why car heater its off and blows hot air?

If a car heater is off but still blowing hot air, it may be due to a malfunctioning thermostat or a stuck heater control valve, allowing hot coolant to circulate into the heater core. Another possibility is a faulty climate control system, where the controls fail to shut off the heater completely. Additionally, a problem with the blend door actuator could cause hot air to mix with the cold air, resulting in warm air being blown even when the heater is supposedly off.