Have a Wellsaver 20 lb tank. The other day we noticed the water pressure increased quite a bit. Called a plumber we know and he said the tank pressure was too high (45lb setting) and adjusted it for a 30-50 psi system. Can't explain why the pressure settings changed. This worked fine until the next day when the water pressure was low and the pump started cycling off/on every few seconds when water was being used. Checked the tank pressure again and it was back up around 45lbs. When I drained the tank to check the pressure reading I only got about a cup of water to drain. Set the tank pressure at 28lbs and turned the system back on. Worked fine for about 7 hours then the pump started cycling on/off again. Again the tank pressure was in the high 30s. Reset the pressure again for 28lbs ands is working fine again. Seems I have to reset the tank pressure after several our of water usage. It is attached to a Culligan N8 water softener.

Any suggestions on what's going on? Tank appears to be OK, no water coming out of the air valve, tapping side indicates it's not water logged. Pump appears to be running fine. Waiting for the plumber to get back to me.

The tank pressure will vary while the system is on. As the pump fills the tank with water, tank pressure goes up. When the pump cuts off, pressure will drop as water is used. Setting the tank pressure should always be done with the system off and the pressure drained to zero by turning on a low level faucet until the system pressure drops to zero. Then you set the tank pressure by using the air valve at the top of the tank. In your case, it should be at 28#.

As to why the pump is short cycling, that is generally the result of a waterlogged tank, but if that is the case it will do it every time when water is being used, not just occasionally. That being the case, it is hard to say what is causing your problem. I think your plumber will start with the pressure switch and then look at the pump. I'd like to see if the pressure switch itself is causing the short cycling, or if that seems to be a pump issue.