I have one which I really like but it acts up sometimes. They have limit switches behind the panel. Could be an adjustment where something is bent and not contacting the switch or a bad switch. Taking it all apart, cleaning, and putting it back together again (which is much harder to do) is frustating when you don't fix it. Mine has an intermittantly bad switch which works when you give the spot next to it a rap with a knuckle.
Also everything modern from appliances to car trim has hidden screws and snaps and there is always a secret way to getting something apart and back together again with out breaking something. I'm not the luckiest at knowing all those secrets.