The system has an amperage/current kickout. So when you run the cover open and it stops it, you can't go that direction again (which is what you want it to do to clear the obstruction...pulling back too much water would be a good example, if it is enough water to cause damage to your system, it will shut itself off). You have to trick it by closing it for a second, then the you can open it. You could also cut off the power to accomplish the same thing, but that's an unnecessary step.
