Another possibility is that one or both of the dryer's electric solenoids need to be replaced. The solenoids open the gas valve to allow the gas to flow into the burner assembly.
It is also possible that the igniter or heating element has burned out. To check both of these parts for continuity, use an ohm meter. It is necessary to replace rather than repair these dryer parts when they burn out. The same is true of the heating element assembly.
A less common problem is that the flame sensor may have burned out, in which case, it must be replaced. Flame sensors are used in gas dryers to detect heat produced by the flame and should be checked for continuity if the dryer fails to heat properly.
Other less-common issues are defective high light or cycling thermostats. The cycling thermostat regulates the temperature of the air in the dryer.
The last items to check, if all else fails, are the main control board and the timer, although these components are usually not at fault when a dryer fails to heat.Learn more about Washers & Dryers