A bathroom radiator may stay on if airflow is restricted, if the valves are stuck open, or if the radiator needs a replacement part or repair. Radiators may also remain on if they are exposed to a draft.
The thermostat may need to be tightened or replaced if the radiator won't turn off. Replacing the thermostat may be necessary if the thermostat is tightly secured to the thermostatic valve body but the radiator still isn't responding to setting changes, according to Shadlock.
The location of the radiator may affect its performance. If the radiator is located under a window or in a cold, drafty corner of the bathroom, insulating the room to prevent drafts may improve the radiator's performance. Radiators also need adequate airflow to maintain optimal performance. When a radiator doesn't turn off, move furnishings and other items at least 18 inches away from the radiator to ensure proper airflow.
The pin located in temperature valve is a common problem, particularly with older radiators. Check the pin to see if it is stuck or damaged and replace as needed. Shadlock recommends cleaning radiators on a regular basis to identify rusted or damaged pin mechanisms early in the season. A radiator that remains hot, even in the off position, may be the result of overflow from the hot water tank. Turning the hot water heater down to a lower temperature, if possible, will prevent hot water overflow into the radiator.