Residential well: pump runs continuously
My system is four years old. Suddenly, my submersible well pump started running continuously even though there was no draw on water. A repairman dug up all around the buried (small) tank and connections and found no leak. He checked the pressure in the bladder tank and it was 22 PSI. (If I get some of the terms wrong, it's because I am thoroughly unfamiliar with well terms.) Then, he changed the checkvalve, and the pump worked fine - for about two hours, after which it started running again. I closed all the valves to the house and irrigation system, but it did not stop. (I know there is no leak under the house because the solar panel would have drained after I isolated it if there were.) He came back and lowered the pressure via the pressure control switch, saying that there must be a link in the well casing. He suggested that they can put in some kind of plastic tubing and also suggested that, at the same time, the pump be replaced. I asked why replace a working pump - is there something better? He said there wasn't but that it was kind of an insurance and I'd be guaranteed at least 5 years of trouble-free operation. He quoted about $1800 with the pump price being around $800 of that for a 1 hp pump.
Now, as a woman (a senior at that), I am skeptical. We do have hard water, but would that cause the casing to leak after only 4 years? I am not convinced as well that I should buy a new pump. Can someone enlighten me? Thanks