If your Dryer Timer does not advance, in other words the timer knob does not move from where you set it at the beginning of the cycle. This symptom typically happens in one of the many types of “Auto Dry” Cycles, which would be any cycle that does not have a time limit shown on the control panel. (i.e. 50 minutes or 20 minutes). Try running the dryer in both the "Timed Dry" as well as the "Air Fluff (aka "No Heat) cycles to see if it will advance.
#1 If Timer advances in the “Timed Dry” or "Air Fluff" cycle: The issue is (most likely going to be the cycling thermostat. Important, if your dryer doesn’t specifically say “Timed Dry” for one of the cycles, then try running each cycle option and note if the timer advances in any cycle. When a timer advances forward, it is the timer's motor that is advancing the timer (dial) forward through the cycle. When the timer is running in one of the “Timed Dry” settings, power is constantly supplied to the timer motor and it advances at a consistent rate from the beginning to the end of the cycle. Therefore, if your dryer timer advances in the timed dry or air fluff/no heat cycle (or another cycle if your dryer doesn’t have a “Timed Dry” cycle), then you know that the timer motor is working and you can eliminate it as a possible cause for the timer not advancing. On any of the “Auto Dry” cycles, the power for the timer is routed through the cycling thermostat, which will supply and cut off power, slowly advancing the timer until the dryer senses that all the moisture is gone and then the timer will move towards the “Off” position. If the cycling thermostat (typically located on the blower wheel housing) fails, power will not be supplied to the timer motor in any of the “Auto Dry” cycles and thus the timer will not advance. To see how to easily test your thermostat, watch the following video and fast forward to 4:38
#2 If your dryer Does Not Advance in the “Timed Dry” cycle and Does Not Heat, If your dryer is Electric, your issue could be that you are not getting a full 240V to your dryer. This is caused by one of the lines coming into the dryer is bad. The source of the issue could be at the terminal block, the dryer cord, the wall plug in or the breaker. Watch the 1st video that will walk you through testing for a full 240v. If you get a positive voltage reading after testing everything shown in video #1, watch the second video.
#3 If your dryer Does Not Advance in the “Timed Dry” cycle and Does Heat. The issue might be a bad timer motor. Watch the following video on How to test the timer motor. IMPORTANT: #1 The video references a resistance range, depending on the style of timer motor is on your timer, this reading could be much lower than stated in the video. #2 In order to get a proper reading, you will need to have your multimeter set to AT LEAST 10K ohms of resistance. If you have it set to the lowest setting you will not get a reading, even on a good motor.