If the door hits the floor and then reverses it is traveling too far in the down direction. Here is the way it works. When the door hits the floor, the motor stalls and the interrupter cup quits spinning and the RPM sensor board quits sending a pulse to the logic board. The logic board reverses the motor and the door opens. What needs to be done is figure out why the 'down limit' is not working or if it is just out of adjustment. The easiest way to do this is remove the cover of the motor unit and watch the limit switch assembly while the door is closing. Turn the down limit several turns in the opposite direction of the arrow printed on the cover. This should get the door to stop short of hitting the floor. Now some tweaking will be involved to get it right. You have it right about the thermal protector. It is to protect the motor from over heating and sometimes seems a pain you know where.

If it is stuck in the open position you will most likely find the trolley is jammed against the bolt just in front of the motor unit. You will need to loosen the chain enough to release the tension and then run the opener until the door closes. While the door is closed locate the 'up limit' on the side of the motor unit and turn this control 2 full turns in the opposite direction of the arrow printed on the cover. Tighten the chain.

Sounds like your receiver has quit. Hard wired wall control and keypad doesn't use it so it keeps working. Time for a new opener. That one is old and outdated anyway.

The solution posted by GDS above was right on. When you come home and find your door open and you know it was closed before you left earlier, then depending on whether the light (clicker) is flashing or not, you have a good idea where to start looking for a solution. No clicking means that the door was ordered to open while you were away either by a stray radio signal with concidental code, a faulty manual push-button switch wired directly to the opener, or stray electro-static/magnetic interference causing an overly sensitive circuit board to behave eratically. A clicking light means that the motor came on by itself without any 'real' external command and attempted to push the closed door even harder against the garage floor and this triggered the overload protection which caused the door to open and the warning light to flash. GDS explains perfectly why the motor would spontaneously come on by itself without any remote command. The reason as reported above is that there is a double-throw,single-pole metal leaf switch (3 thin metal strips riveted together) which gets activated only when the door moves to its fully open or fully closed position. One switch, two roles to play, thanks to two plastic wands that move up and down with the motor to trigger a stop at either the upper or lower pre-programmed positions. This leaf switch is soldered to the circuit board by 3 joints, and over 16 years in my case, the constant pressure on this leaf switch (several inch-ounces of torque) can cause the solder joints to crack. And so they did in my case, as you need a magnifying glass to see these hairline cracks, but they were apparent to me, having worked in electronics for over 40 years. When wind vibrates the garage door, the vibrations feed back into the circuit board and the bad solder joint(s) temporarily opens the circuit which makes the motor think that it still needs to continue closing the door. Since the door can't be physically moved any more in the down direction, the safety micro-switch gets triggered by the overloaded motor and the door gets re-opened. To repair the bad solder joint(s), you need a 50 watt electronic technician's pencil shaped soldering iron and some thin solder that is designed for electronic work and not for copper plumbing. Overheating the solder tabs on the board will cause delamination. Better to let an expert do the work. Cheaper than replacing the whole board and in my case, I only needed an hour to solve this problem, which would have been impossible without this thread. Thanks GDS. All problems in life should have a posted solution like this one.