I just purchased a house that we are fixing up to move into(note this house is 7 hours away from where we live now). There is a well on the property and a new pump was installed approx. 1 year ago. Upon getting there, the well power was off, so we put the fuse back in and turned it on. It continued to shut down and the guage was registering zero. We went ahead and replaced the pressure switch with the same model(30-50 Square D) and guage. After the tank was drained, we checked the pre-charged pressure and it was 28 psi. We capped off the outgoing pipe as we plan to replace the underground supply from galvanized to pex. We turned it on and it built pressure to 60 psi then the pump stopped. We were happy with this and figured we'd just adjust the switch to 50 psi and be done. I turned off the power, and over the next 5 minutes the pressure began to rise and according to the gauge it went to over 100 psi. I also tested it with a hose bib tester and it read the same. I knocked on the tank once it was filled, and it sounded like the top was still hollow. My question is why would the pressure slowly and steadily rise 40 psi (maybe more if I hadn't began to drain it) after the pump had stopped? Other things to note are that we had a 100ft hose connected to it, the water was pretty cold, it was about 70 degrees outside that day, and the pressure tank is an amtrol well-x-trol and is approx 70-80gal. Also, we continued to use the hose for quite a while with good pressure, which leads me to believe that the pressure tank is working. Any advice is appreciated.

From what you have described, it could not happen. Pressure does not come from nowhere, it has to be introduced to the system, and once the pump stopped, if it really did, it could NOT raise the pressure any further. The tank also can NOT increase the pressure above what its air charge is.

This is what I do not understand, I feel completely stupid trying to figure this out(the human factor). I'm going to be back up this weekend and test it. Can a bad tank cause any pressure increase or are there any factors that can add to pressure rise?

The tank cannot physically "increase" the pressure higher than the pressure of the air's precharge. Nor can anything else raise the pressure unless something is pumping in to it. If what you describe were possible, and you could "bottle it" people would not need pumps.

If the 100' hose was pressurized because the valve at the tank was left in the open position (assuming there was a hose nozzle on the other end) and the hose was exposed to the sun, the heated water would make the pressure increase.

About 80 feet of the hose was in the 70° Sun. Do you think it could raise it that much in a small amount of time?

I'd guess that the pump was still receiving power. The valve you turned off wasn't between the pump and the switch was it ?

We didn't turn a valve off, but we did cap off the outgoing supply. I'll do more testing this weekend and report back.

The amount of pressure increase would depend on the size of the storage tank, but in most cases would be negligible.

NO, and if the hose valve had the required backflow preventer, it would not have happened in the first place.

Most hose bibbs at the tank manifold are not back-flow protected; usually, they are 'boiler drains'.

Well is all fixed! The problem was a very clogged nipple that holds the pressure switch. Thanks for all the suggestions, I appreciate it.