Answer: -It sounds like maybe the check valve is defective. That part is available separately and is not expensive. Yes it will damage the motor and other parts. I don't know how they have this set up. I would think that it would not be too hard to arrange something that would both block the air and still allow for drainage. They may have already set up something. -If the pump is pumping water when it is running, then it is working as it should. A sump pump turns on when the water reaches a 'trigger' level, and then turns off when the water is below the low limit of the pump. If it keeps cycling like you say it is doing and it is pumping water out, then when the pump has pumped out the water down to the lower limit and shuts off, within a minute, more water has entered the hole and has reached the 'trigger' level, turning the pump back on. These continuous short cycles will certainly not add to the lifespan of the pump. You say water cannot get into the hole with the plexiglass cover over it. Then where is the water coming from? If your pump is actually pumping water out every minute or so, and there is no floor water flowing into the pump hole, I would assume that ground water is perculating up into the hole almost as fast as the pump is pumping it out. This seems like a "Catch 22" arrangement. The hole is needed for the sump pump to pump the water out of the hole, but the hole is allowing ground water in at almost the same rate. In that case, something to plug up the hole under the pump makes even more sense. You can use a hydraulic cement (like Drylok's 'Fast Plug') to form a 1" or 2" plug for the ground water. Hydraulic cement works even under water pressure and expands as it dries (5 minutes), forming a tight bond in the hole. This will also take care of the radon problem. After it dries, sit the pump on top of the plug to allow it to do what it was intended to do.