Dave Liquorice presented the following explanation :
>> The controller has crashed a couple of times over the years, failing to
>> work via the remote, which has meant my entering by another door to
>> reset it.
>
> How would you reset it if there is no "other door" to allow access to
> the control unit if the door won't open?
I suppose I could switch off the main supply to the garage to reset the
controller's processor, but all of the electric door makers seem to
have a manual cranking system built-in by default in case the whole
thing dies or their is a power cut.
Where there is no 'other door', they suggest you install an add-on to
link the manual cranking system to the outside of the door.
Mine runs on 24v DC, so I could add some back up batteries, but over
the years we have had it, not once I we had a power cut, when I have
needed to operate the door. I did once test the hand cranking system,
just to see it worked when I first installed it - its a bit of a PITA
compared to pressing a button, but it works.
Mine came with two remotes, one in the house, one in the car. I soon
added a third wired remote (up/down/stop) in the garage. I then later
added a beam sensor across the door level with my car's tow ball, to
prevent the door closing unless the ball was clear of the door. It's
red LED also serves as a means to see when parking that I have stopped
clear of the door.