Symptom:
Pump runs, but will not build up pressure. It does deliver water.

Hardware:

Pump: Flotec 3/4hp Shallow Well Jet Pump
Tank: FP7120 (35 gallon that is supposedly rated at 82 according to their literature)


I recently put this pump in -the old one burned out. Here are the installation particulars:

1" PVC pipe down in the well to a depth of 25' - foot valve at bottom. (I would have put the recommended 1.25" pipe down the well, but the idiots who put the last pump in dropped the original submersible pump down in the well while trying to replace it. Now only a 1" pipe can pass by it and reach the watertable).

1" PVC on output.

The pressure switch is set to 30/50, the tank pressure is at 28psi.

The pipe goes from 1" to 3/4" pipe in order to feed the water softner. The output of the softner goes back to 1" for the run to the house (20'), then goes down to 3/4 copper.

After first replacing the pump - it ran as advertised for two months. Then it would constantly cycle off and on and eventually the gauge would run down to zero (or a very low pressure) though the pump would be running constantly. Water would either be a trickle or nothing at all.
Upon checking the tank, I found that it had gone bad, so I replaced that - It ran for a few hours fine, then started having the same symptom of running constantly though not building up any pressure.

Any advice / help is appreciated.

Thanks.