Diagnosis
Restricted airflow. The most common culprit is a clogged vent hose or external duct, not the internal lint filter.
How to Fix It
Disconnect the flexible vent hose from the back of the dryer. Check it for massive lint buildup, crushing, or kinks. Then go outside and check the exterior wall vent flap—it should open freely when the dryer runs. If airflow seems weak, the duct itself needs professional cleaning.
If That Didn't Work
The heating element can be failing intermittently. While the dryer runs on a high-heat cycle, feel the exhaust air at the back after 10 minutes. It should be very hot. If it's just warm, the element or its thermal fuse may need replacement.
Heads Up
Running with a clogged vent is a major fire hazard and overheats the dryer's components, causing more expensive failures.