Heat is the system that fails most often, and electric and gas dryers make it in different ways. An electric dryer runs a coiled nichrome element on 240 volts; the coil can break, sag against its housing, or burn through at a terminal. A gas dryer uses a burner assembly: an igniter glows, a flame sensor reacts to its heat, and the gas valve coils open so the burner can light. Weak valve coils are a classic gas-side fault, showing up as a flame that lights, drops out and struggles to relight. Either way, the result at the laundry basket looks the same: the drum tumbles and the load stays cold or damp.
Wrapped around that heat source is a set of control and safety parts. A cycling thermostat, or on electronic models a thermistor read by the control board, holds exhaust temperature in a working range. A high-limit thermostat opens if the heater housing overheats and closes again on its own once it cools. A thermal fuse, and on some designs a separate thermal cut-off, is one-time protection: once it opens it stays open. Depending on the model, a blown fuse removes only the heat or stops the whole dryer. These parts rarely fail by themselves. They usually open because hot air had nowhere to go, which is why the vent is always checked alongside them.
The drive side is mechanical. A motor turns a long ribbed belt that wraps around the drum, and a spring-loaded idler pulley keeps tension on it. The drum rides on rollers, on plastic or felt glides at the front, or on a rear bearing shaft, depending on the design. The same motor usually spins the blower wheel that pulls air through the drum and pushes it out the vent. When rollers wear flat or a pulley bearing dries out, the dryer gets loud before it quits. When the belt snaps, the motor may keep running while the drum sits still, and some models shut the motor off through a belt switch.
Airflow ties every other system together. Air enters the cabinet, passes the heat source, moves through the tumbling load and the lint screen, then into the blower and out the exhaust duct. Anything that slows that path, whether a packed lint screen, a crushed foil transition hose, a bird nest in the wall hood or a roof cap matted with lint, makes the dryer run longer and hotter. Longer and hotter is what cooks thermal fuses and bakes the lint that collects inside the cabinet. Lint burns easily, and a badly restricted dryer is a genuine fire risk rather than a theoretical one.
The last group is control and sensing. A door switch tells the dryer it is safe to run, a push-to-start switch or a keypad button starts the motor, and a mechanical timer or an electronic control decides how long the cycle lasts. Moisture-sensing models use two metal bars near the lint screen, and the control reads the tiny current that passes when damp clothes bridge them. Fabric-softener film coats those bars and makes the dryer quit early. Electronic boards and their relays can fail after power surges or years of heat, but they are checked last, after the cheaper parts that commonly cause the same symptom.
