If the timer not heating is the problem, you will need to check the timer contacts for continuity. To do that you will need to use a multimeter.
Disconnect the dryer from the wall outlet. remove the controls back panel, set the multimeter on the lowest scale to read ohms and the timer on a drying cycle.
Disconnect the black wire from the timer. Take a reading between the terminal that you just remove the black wire and the terminal with the red wire connected to.
The reading should be close to 0 ohms, if the reading is infinity the timer contacts are bad and the timer needs to be replaced.
To replace the timer do the following. Remove the timer knob, remove holding screws and remove the timer with all the wires attached to it. This way it will be easier to install the wires to the new timer.
Remove the wires one by one from the bad timer and install then to the new timer until you have replaced all the wires.
Set the timer in place and secure it with the holding screw. Install the controls back panel and the timer knob.
Make sure you view my video a few times until you know for sure that you know how the repair is done.
Below are the links to the parts needed for this repair.