How to test the power supply for the heater in an electric dryer for both L1 and L2
OK ... this is dangerous, but this is what I would do to narrow it down. Essentially we want to find out if power is being supplied to the element from L1 or L2 or both when it is off. You have to be very careful doing this - consider yourself warned ... 240v will do damage to you.
***Unplug the dryer.***
Take one of the red wires off of the heating element - does not mater which one. Bend it out of the way so that it is not close to any ground.
Plug dryer back in.
Turn unit on - it will not heat, but should be sending power to the red wire you have disconnected and to the terminal that you took it off of. Check that - put one lead on the wire that is out in the open and the other on the terminal. You should be seeing 240 volts there. Now open the door. As you said the element continues to heat even though the unit is not running. Now check those points again. Do you have 240 volts? If not, then check each one to ground. Do you have 120 volts on one side? If so which side? With this information we can decide if the power is coming through the motor (centrifuge switch) or the timer.
Please don't electrocute yourself.
Source: Whirlpool Heat Element Not Turning Off LER7646EQ0