A dryer that takes two or three cycles to dry a normal load almost always has a clogged vent. This is also the single biggest residential-fire risk among appliances — per the U.S. Fire Administration, dryers and washing machines cause an estimated 15,970 residential fires per year, and failure to clean the dryer is the leading factor.
Diagnose it yourself first. Clean the lint screen, then disconnect the vent at the back of the dryer and run a dry cycle. If the clothes dry normally with the vent disconnected, the dryer is fine — the vent is the problem. The fix is a full vent cleaning from the dryer connection through the outside wall termination. Long vent runs with multiple elbows, vinyl flex hose (which should never be used — only rigid metal or semi-rigid aluminum), and crushed sections behind the dryer are all common failure points.
If the dryer still takes forever with the vent disconnected, the issue is inside the machine. A partially failed heating element produces some heat but not enough; a bad operating thermostat cuts heat before the load is actually dry; moisture sensors coated with dryer-sheet residue trigger early cycle termination in sensor-dry modes. All three are diagnosed with the cabinet open.
Annual vent cleaning is inexpensive and addresses the fire risk at the same time.