The 7 most common part(s) or condition(s) which cause the symptom Dryer won't stop are listed below starting with the most likely. Check or test each item and watch any available videos.
The most common problem when a dryer is slow is when the vent is clogged. If the dryer is slow, check the vent from the back of the dryer to the outside of the house. If that is clogged, clear it completely and test the dryer. If the dryer is slow after the vent is cleaned, clean the internal ductwork of the dryer. This will require some disassembly.
RepairClinic Item # 687613
The blower wheel draws air through the dryer and pushes the air out the vent. If the dryer won't stop, the blower wheel may be plugged up or not be spinning properly, which reduces the air flow. Check to see if the blower wheel is securely fastened to the drive motor shaft.
RepairClinic Item # 525502
The heating element assembly warms the air before the air enters the dryer drum. If the dryer won't stop, it may be because the heating element assembly isn't working - which greatly increases the drying time. Check the heating element for continuity.
RepairClinic Item # 1206293
Dryer sheets and fabric softener can leave a residue on the lint filter, reducing the air flow. If the dryer won't stop, check to be sure air can flow freely, clean the filter as needed.
RepairClinic Item # 525385
Although not as common, if the dryer won't stop it may be because the moisture sensor is either defective or shorted.
RepairClinic Item # 526282
If the dryer won't stop, check the high limit thermostat. If defective, the high limit thermostat can turn off the heat prematurely, lengthening the time it takes to dry a full load. This is not common.
RepairClinic Item # 1181075
The thermistor senses the temperature of the air in the dryer and cycles the heat on and off. If the dryer won't stop, the thermistor may be defective. This is not common.