I have an HE3 that heats up when turned on, but won't stay hot. We've cleaned out lint & vent(even inside machine),replaced thermostat and back-up/safety thermostat. What else can we try?

either very bad venting and lint build up inside machine and in lint basket? possible vent tube in machine for lint clogged? or bad cycling thermostat located on blower, and hi-lo limit thermostat located on heating element?

Check the complete venting system inside the dryer and to the vent outside. Be sure and check for lint & god knows what around the blower wheel. Get everything 100% clean. Insert a thermometer into the vent coming out of the dryer with the vent hose off. Start the dryer on high heat & see if it will go to not over 180% and start going lower like 130% or so if it drops back it's ok . If it don't stop & go down cycle thermostat is most likely bad. The reason it won't start for an hour may be the motor gets too hot. You could put an ohm meter across the connection on the cycle therm and heat it with a small torch or something & see if it will show open after heating. Just a guess lots of things cause these problems. Clean that motor too. Lint may cause it too run hot.

Try inserting a thermometer in the vent on the back with the vent tubing off . Run it and see if the heating element turns off at 180 degrees or less if not try a new operating thermostat . It's supposed to shut it off . Try this on timed dry if it shuts it off in timed dry may be in the auto dry circuit somewhere.
Be sure the vents inside the dryer and to the outside are completley clean do this first. Check for lint and anything else around the blower wheel.

Sound like thermostat is not working. Should turn off heating elements when drying temp. is reached.

I do not know your definition of "way too hot". Remove the exhaust vent and insert a accurate thermometer in the dryer exhaust. Run the dryer on high heat. The temperature should get up to 165 degrees then cool down to about 125 degrees then back up to 165.
If it goes above 165 and stays there replace the high limit thermostat.
If it cycles correctly it is OK.

have you vacuumed the lint or blown thru from the lint catcher thru the machine into the wall outlet and then even the wall outlet. I found a bunch of lint inside the dryer that could not get out because the vent was plugged almost all the way to the outside wall. My vent has to travel a long way to the wall.
Once I did this, it alleviated the heating up of the dryer

Is it blowing hot air out the vent?. I've seen something like pencils , lint or about anything clog the fan and won't let it turn. The vent must be clean going to the outside of the house. You can take the vent tube off at the dryer and see if it helps if it does out side vent might be cloged.
The operating thermostat might not be cutting off power to heating coil soon enough and getting hot enough to blow fuse. Check all thermostats and any one time cutoffs a one time fuse. Don't know what type dryer or model number you have. When you ask for help always give the name and model or your machine because they are different.Hope this helps.

have u replace heating sensor

It may not be your heating element. Your dryer lint vent pipe out the back of the machine or maybe out the side may be plugged. You have to pull the machine out and clear that pipe or rebuild it out to a soffit vent or static vent if it is in the attic, or out through your crawl space. This will make a huge difference. If that hot air and moisture doesn't get out of the machine it just goes back into your clothes.
Good luck!!

Start with the vent, make sure it's not kinked or squished behind the machine and that the outside vent is not clogged with lint. You should feel air blowing freely to the outside.
If the vent is ok, turn the timer to any on position without starting it. Wait 10-20 seconds and then check if there's heat inside the dryer.
If yes, the element has a short and therefore always stays on. Replace it.
If no, run the dryer for a few minutes and listen for the clicking of the relay which cycles the element.
If there is no clicking sound, check the hi limit thermostat & thermal cutoff for continuity and replace if necessary.
If those seem ok, it could be the motor (centrifugal switch inside) or the timer (shorted contact).
Good luck!

If not