Pump will not shut off

I have a 1/2 horse power jet pump that pumps water from a well to my home. The pump and well are 20 years old and have never given me much trouble until now. The darn thing wont shut off. I have replaced the pressure switch and the water tank (thinking maybe the bladder was leaking) but still it runs constantly. It hasnt taken a break in over a month. I even checked the pressure line that runs between the pump and pressure switch thinking that maybe it was clogged. (It wasnt) Now I'm lost. What else could it possibly be? We still have pleanty of water, no loss of pressure; what gives??

Mark

Older pumps might fail to reach a high-enough pressure to activate the pressure switch to shut down. Also, make certain the tubing/pipe to the pressure switch isn't clogged up.

Then the jet is blocked or the impeller is worn out. The jet is in the wet end of a single line shallow well jet pump and in the j-body in the well if a two line deep well jet pump.