DerbyDad03 wrote:
I could be wrong, but I was under the impression that the pressure type
limit switches only reversed the door when it was on it's way down -
i.e. the motor had to be operating at the time it hit an obstruction.

It would seem to me that if a ground swell could open a door, then
simply pulling up on the handle hard enough would turn the motor on and
open the door at any time. I guess that would be a good test for this
situation. Grab the handle and pull up hard. If the door opens, then
perhaps the ground is causing it to open, but I'd think that would be a
bigger problem than simply the limit switch being close to it's limit.

Art Todesco wrote:
Check the limits. The closed limit is
probably right on the edge of triggering.
Basically, it is probably opening
because it "thinks" there is an object below
the door. That object is probably the
floor heaving up when it gets cold.

mcq142 wrote:
I have Mac Lift Merlin Series that opens on it's own, especially during
the night. It is used on a one car door size. The larger 2 door model
instaledd in the next bay never has this problem. This has only been a
problem during below freezing temps. Thanks, Tom

To me I would think that it would be an overly sensitive door if it
responds to an expanding slab of concrete. I don't think the concrete
would expand /that/ much.