Pump runs and empties tank, bringing it down to zero pressure and water and pump stop. Pressure switch does not automatically click on to restart pump. However, when pressure switch outer case is tapped lightly a couple of times something seems to be jarred loose and switch trips and everything works fine for awhile. Happens every other day or so, getting tired of jumping out of the shower and crawling under the house. Any idea what might cause this intermittent problem and how to fix it?