Start with the cause that costs nothing. On most electric dryers the motor and controls run on 120 volts, but the element needs the full 240, supplied through a double-pole breaker. If one side of that breaker trips, or a fuse blows in an older panel, the drum still turns and the display still lights, yet there is no heat. A loose or burned connection at the terminal block, where the power cord enters the dryer, produces the same result. Switching the breaker fully off and back on is a safe owner check. Anything involving the terminal block or live voltage belongs to the technician.
Next most common is an open thermal fuse or thermal cut-off. These one-time parts sit on the blower housing or the heater housing and open when the exhaust overheats. On some designs an open fuse stops the whole dryer; on others it removes only the heat, which is why it belongs on this list. The fuse is almost never the root cause. It opened because air stopped moving, usually from a clogged vent, a crushed hose behind the machine or a lint-packed heater box, so the technician measures airflow before calling the job finished.
Third is the heat source itself. An electric element is a coil of resistance wire strung on ceramic insulators, and after years of heating and cooling the wire breaks, usually at a hot spot or where it has sagged. On a typical full-size dryer a good element reads roughly ten ohms, and a broken one reads open. On a gas dryer, the igniter can crack and stop glowing, and a flame sensor that fails open keeps the igniter from getting power at all. If the igniter glows and then goes dark without the burner lighting, the gas valve coils are the usual suspect; if it glows steadily with no flame, the flame sensor is.
Fourth come the thermostats and sensors that switch the heat. A high-limit thermostat that has opened and will not close again cuts heat completely. A cycling thermostat, or on newer electronic models a thermistor, tells the control when to turn heat on and off; a failed one can stop the call for heat or make the dryer short-cycle so badly the load never warms. On electronic dryers, a heater relay on the control board can burn its contacts and stop switching the element. That is a less common failure, and it is diagnosed only after every part in the series chain tests good.
Gas dryers add one more link: the fuel. A quarter-turn valve on the supply line behind the dryer must be open, with its handle parallel to the pipe. If it was bumped during a move, a remodel or a water-heater swap, the burner never lights. A kinked flexible connector or a dryer set up for the wrong gas type can do the same. If there is any smell of gas, do not try to diagnose anything: leave the house, do not operate switches, and call PG&E from outside. The technician never works on a gas dryer until the supply is confirmed safe.
