Leaving a radiator heater on all night is generally not recommended due to safety concerns. While radiator heaters are designed to provide efficient and consistent heat, continuous operation for long periods can pose fire risks and increase the chances of overheating. Additionally, leaving a heater unattended while sleeping can lead to accidents or unwanted incidents. It is advisable to follow manufacturer instructions and use built-in timers or programmable thermostats to regulate the heating duration or maintain a comfortable temperature.