I have a 1/3 hp jet pump in boathouse and it wont shut off. It builds up about 20 lbs pressure and keeps running but wont build up to 40 like normal. I changed foot valve in lake. The switch will open and close fine(points are clean). put new pressure guage on. could it be the bladder tank or the pump. i heard there is a rubber part in the pump that wears and can be replaced. Need help please Todd