The 6 most common part(s) or condition(s) which cause the symptom Dryer takes too long are listed below starting with the most likely. Check or test each item and watch any available videos.
If the dryer takes too long to dry check the venting system. A clogged or partially clogged vent from the dryer to the outside will reduce the air flow through the dryer and greatly increase the drying time.
RepairClinic Item # 686172
If the dryer takes too long to dry the blower wheel might be broken or plugged. The blower wheel in the dryer is attached to the drive motor and draws the air through the dryer drum. Remove the vent from the back of the dryer and see if the air flow is strong. If not, check the blower wheel.
RepairClinic Item # 3479
Gas dryers have a two or more gas valve solenoids. If the dryer takes too long to dry it may be because one or more of these solenoids has failed. These coils often fail intermittently. If the igniter lights up and then goes out without igniting the gas, replace these coils as a set.
RepairClinic Item # 2708
Although not common, if the dryer is slow check the lint filter. The lint filter can get clogged with fabric softener and not allow enough air to pass through. Clean the filter of any residue that might prevent proper air flow.
RepairClinic Item # 2933
All dryers have a high-limit thermostat to help prevent fires and damage to the dryer. If the dryer is slow, it can be caused by a defective high limit thermostat turning off the burner prematurely. This is not common.
RepairClinic Item # 2893
All dryers have a thermostat to regulate the temperature of the air. If the dryer is slow it can be caused by a defective cycling thermostat. This is not common. Check the venting first before replacing a cycling thermostat. A cycling thermostat has normally closed contacts that open on temperature rise. Some thermostats have a bias or "cheater heater" built into the thermostat to add heat so the thermostat will cycle sooner to get the lower temperatures. This heater if applicable will be the smaller terminals in the center. The thermostat and heater can be checked with a meter.