A dryer that has no heat may need the heating element, high-limit thermostat, cycling thermostat or igniter replaced. The radiant-flame sensor, coils, temperature sensors or timer may also need to be fixed.
If the dryer is electric, the heating element may be defective if it is not producing heat. This can be measured with a multi-meter. If the test fails, the heating element is the problem. The high-limit thermostat may also be failing if a dryer cannot produce heat. This is a safety device that prevents overheating. Often it is tripped due to a clogged exhaust vent, so individuals should check the vent if a dryer is not heating.
The cycling thermostat controls the temperature in the drum, and it can fail over time. This can be checked with a multi-meter, but individuals should ensure the dryer is unplugged before checking. If the dryer is new and gas-powered, it may not heat due to the igniter being faulty. Again, this is a part that can be checked with a multi-meter.
If none of these parts are the culprit, an individual can check other parts of the dryer such as sensors, coils and timers. If unable to find the reason for failure, contact an appliance repair professional.