I have a submersible pump in a reservoir, the reservoir has plenty of water. I have a pressure tank set at 30/50, I have watched it run through some cycles. It first comes on at 30 then cuts out at 50, next time it comes on at 25 and cuts out at 45 and then the next time it came on at 25 and then quit at 40, I noticed that after 1 minute it resumed pumping up to 50 and stopped. I realized that the pressure gauge contacts had still been closed but the pump had stopped pumping and then rested or cooled and then finished pumping up to where it was supposed to cut out. The pump does have a thermal switch but it is in a large reservoir of 50 degree water. What is happening?