My submersible pump in a shallow well/spring won't shut off causing water pressure to go above 100psi until pump probably overheats and shuts down. I am not sure what causes it to shut down but I suspect their is some kind of over temp protection system. I think the pump is a Franklin 3/4hp 230 volt. I thought the problem was the pressure switch, a square D, and replaced it but found that the points were closing at 20psi and opening at 40 psi as it should but pump continues to run building pressure. I am able to turn off pump with circut braker to pump.

It does not do this every time but pump cycles a time or two normally then has this trouble and continues to run. Also, if I bump the open contact points on the pressure switch closed then open when it is going over the pressure limit it will flash something and the pump will shut down and pressure drops until 20 psi and starts over again like normal.

I replaced the control unit with a Goulds unit for a 3/4 hp pump that I had around from another well but problem remains the same. Orginal unit was a Franklin Electric 2801074915.