Dryers fail in predictable ways: a heating element opens, a thermal fuse blows, a belt snaps, or the vent clogs. The vent is the single most common cause of every other problem — restricted airflow makes the cycle hotter, which trips the fuse, kills the element, and roughly doubles the energy bill. Always disconnect power before service. If you have a gas dryer, also shut off the gas line at the valve.
On an electric dryer this is almost always a blown thermal fuse (one-time, in the blower housing), a failed heating element, or a tripped high-limit thermostat. All three are caused by restricted airflow — fix the vent before you replace the parts or you'll be back here in six months. On a gas dryer the suspect is the igniter, the gas valve coils, or the radiant flame sensor; the igniter glows orange for a few seconds and then the gas valve opens.
Vent restriction. Pull the dryer out, disconnect the duct from the back, and run a load — if it dries normally, your duct or wall vent is clogged with lint. Clean the entire run from the dryer to the outside hood. Long horizontal runs and flexible foil ducts are common offenders; replace foil with smooth-wall metal. Clean the lint trap before every load and pull out and vacuum the trap housing twice a year.
On most models the door switch must close, the thermal fuse must be intact, and the start button must complete a circuit through the motor centrifugal switch. Listen for a click when you press start: a click with no spin is usually a seized motor, a broken belt that lets the motor free-spin (some models have a belt switch that prevents start), or a tripped thermal fuse. No click is the door switch, the start switch, or the timer.
Snapped belt. Most belts are 1/8 inch by 92 to 95 inches and cost under twenty dollars. Replace the idler pulley while you're in there — they wear together.
Drum support rollers (rear), front drum glides, or the idler pulley. Rollers are the usual cause of thumping; glides squeak. Replace in pairs/sets — the parts are cheap and you don't want to be back inside the cabinet.
The high-limit thermostat is failing closed, the cycling thermostat is sticking, or the moisture sensor strips inside the drum are coated with fabric softener residue and reading dry too soon. Clean the sensor strips with rubbing alcohol every few months.
Stop immediately and unplug. Pull the lint trap and shine a flashlight down the cavity — if you see lint accumulation around the heating element, you've been one cycle away from a fire. Vacuum the entire blower housing, replace the thermal fuse, and inspect the element for distortion.
Vent is dumping inside the cabinet — duct came loose at the back, or the vent is so clogged the moist air can't escape. Inspect the duct connection; clean the run.
Look up the code in the service manual for your specific model. Most error codes on dryers point to thermistor failures, moisture sensor faults, or motor tachometer issues, and the manual lists the resistance values to test for.
Flame sensor — a small disk near the burner that detects the flame and tells the gas valve to stay open. They fail closed (no ignition) or open early (short flame, then off). Inexpensive part, fifteen-minute replacement.
Gas dryer issues with the gas valve itself should go to a licensed technician — open gas valves with a leaking solenoid are a fire risk. A burning smell that returns after vent cleaning means the wiring or motor is failing.
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