Hello I have a whirlpool dryer model leq9508pwo. It stoped heating, In testing it I found that the thermal cut off was open. I replaced the thermal cut off, the hi limit thermostat and the dryer cycle thermostat and the heating element was working how i did not work very long, not even one load, now the thermal cut off is open again. can you tell me what may be causing this problem.

Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it so the thermal cut-off blows.