Shallow Well Jet Pump Chatters and Won't Shut Off: Check Valve or Pressure Settings

1/2 HP shallow well jet pump fills pressure tank but then chatters ("diesels") instead of shutting off. New pressure switch and tank pressure check didn't help.

Two Likely Causes

1. Leaking check valve: "When this happens the water fills the tank then immediately runs back down the well. The switch responds to the low pressure and starts again. Over and over."
2. Pressure switch vs. tank pre-charge mismatch: "With pump off and system drained, tank pressure should be 3-4 psi under the pressure switch cut-in setting. Example: pump starts at 32 psi → tank should be 28-29 psi."

Both cause rapid cycling. The check valve is the more common culprit on jet pumps; a slow leak back down the drop pipe makes the pump short-cycle continuously.