I have two, 6 year old Overhead garage door openers. On about 5 occasions in the last couple of months, I have discovered one side has opened on its own. When this has happened, neither of the manual switches will function, but the RF openers will operate the door in either direction. I have checked the Safety Beam for obstructions and found none. Any ideas? I am thinking along the lines of an intermittent short in the circuit board of the opener but would welcome any thoughts or ideas.
The fact that it's intermittent makes it hard to prove. I suspect the manual switches you refer to are the type with a separate up button and down button rather than a single button type control. If that is the case then I suspect the up button (or the wires from it) has made a connection (short). That would explain it not working when you push the down button because the up is still in effect pushed. It could also be as you say a short in the board giving the signal to open. Some openers have a push button on the board also. I would try disconnecting the wires at the opener going to the manual controls. If it works for a month or two without any problems then I would replace the switches.