Well Pump Short Cycles Tank Versus Leak Versus Switch Decision Tree

Why this matters

A well pump that snaps on and off every few seconds is destroying itself; motors and control contacts are rated for a limited number of starts, and rapid cycling burns both fast. Three causes dominate: a waterlogged pressure tank that has lost its air charge, a system leak (foot valve, check valve, drop pipe, or above-ground line) that bleeds pressure, and a pressure switch fault (bad setpoint, pitted contacts, or a clogged sensing port). Each has a distinct test, and replacing the wrong part leaves the pump cycling and the customer paying again. The discipline is to read the tank's air precharge, watch the on/off pressure behavior, and isolate leak versus switch before condemning anything.

The decision flow at a glance:

  Well pump short-cycles - tank, leak, or switch?
  |
  +-- 1. Tank thuds solid? ----------------> WATERLOGGED
  |                                          TANK
  |
  +-- 2. Pressure decays with pump off? ---> LEAK: foot
  |                                          / check /
  |                                          drip
  |
  +-- 3. Precharge good, no decay? --------> PRESSURE
  |                                          SWITCH
  |                                          FAULT
  |
  +-- 4. Constant-pressure (VFD) system? --> DRIVE /
  |                                          TRANSDUCER

Symptom presentation

The pump cycles on and off rapidly, often audible as repeated clicks at the pressure switch and quick pump starts. Variants: cycling that worsens when a fixture is open (small drawdown then immediate restart points to lost tank air); cycling even with NO water being used (a leak bleeding pressure, or a switch sensing fault); cycling with a normal-feeling tank that thuds solid when tapped (waterlogged tank); cycling with erratic gauge swings or chattering contacts (switch problem). A tank that feels heavy and full of water with no air cushion is a top suspect.

Quick checks

• Tap the pressure tank top to bottom. A waterlogged tank sounds solid (water) most of the way up instead of hollow (air) in the top third.
• With power off and system drained to zero pressure, read the tank's air precharge at the Schrader valve. It should sit about 2 psi below the pump cut-in pressure.
• Watch the gauge: note cut-in and cut-out pressures and how long the pump runs versus how fast it restarts.
• With the pump off and a fixture closed, watch the gauge for pressure decay. Pressure dropping with everything closed indicates a leak (or a check/foot valve not holding).
• Inspect the pressure switch contacts and the sensing tube/port for corrosion, pitting, or scale clogging.

Isolation tree

Branch 1: Tank thuds solid, precharge LOW or absent. Waterlogged pressure tank. With no air cushion, even a tiny draw collapses pressure and the pump restarts immediately. This is the most common short-cycle cause. A bladder tank with a failed bladder will not hold precharge; a non-bladder tank has simply lost its air charge.

Branch 2: Pressure DECAYS with the pump off and all fixtures closed. A leak. The decay rate and where it stops tell you where: pressure falling toward zero suggests a failed foot valve or check valve letting water drain back down the well; pressure falling to a partial level suggests an above-ground leak or a slow drip. The pump restarts to replace lost pressure even with no demand.

Branch 3: Tank precharge correct, no pressure decay, yet cycling persists. Pressure switch fault. Suspect a switch differential set too narrow, pitted/welded contacts chattering, or a clogged sensing port giving the switch false rapid readings. The mechanical system is sound; the control is misbehaving.

Branch 4: Cycling only under flow, tank and switch nominal, but a constant-pressure (VFD) system. A VFD/constant-pressure controller fault or a fouled transducer can mimic short-cycling. Diagnose at the drive, not the switch.

Confirming diagnosis

For the tank (Branch 1), drain the system to zero, then read the Schrader precharge. A reading far below the cut-in pressure (it should be roughly 2 psi under cut-in) or a tank that will not hold added air confirms a waterlogged tank or failed bladder. Recharge a good non-bladder tank and re-test; if it short-cycles again within minutes, the bladder/air retention has failed and the tank needs replacement.

For a leak (Branch 2), pressurize the system, shut the pump off, close every fixture, and watch the gauge over several minutes. Steady decay confirms a leak. Isolate above-ground by closing the valve at the wellhead/tank tee: if decay stops, the leak is downstream in the house; if decay continues with the well side isolated, the foot valve, check valve, or drop pipe in the well is leaking back. A submersible system that loses prime overnight points to a failed check/foot valve.

For the switch (Branch 3), with a verified-good tank and no decay, observe the contacts. Chattering, pitted, or welded contacts confirm a switch fault. Pull and inspect the sensing port/tube; scale or debris clogging it produces erratic, rapid switching. Adjusting the differential to the proper spread (cut-in to cut-out) and cleaning the port, then re-watching the cycle, confirms the switch as the cause when cycling resolves.

Remediation

• Waterlogged tank: Recharge a non-bladder tank's air to about 2 psi below cut-in; replace a bladder tank with a failed bladder. Size the tank for adequate drawdown so run cycles meet the minimum-run-time guidance for the motor.
• Foot/check valve or drop-pipe leak: Replace the failed foot or check valve; repair the leaking drop pipe or above-ground line. Restore the system's ability to hold pressure with the pump off.
• Pressure switch fault: Replace a pitted/welded switch, clean the sensing port, and set the differential to the OEM spread. Confirm clean cut-in/cut-out cycling.
• VFD/constant-pressure fault: Diagnose and service the drive or transducer per the controller manual.

References

• Franklin Electric and Goulds (Xylem) submersible well pump application manuals, on short-cycling causes and minimum run-time / pressure-tank sizing.
• WellMate / Amtrol pressure tank manuals, precharge setting (cut-in minus 2 psi) and waterlogging diagnosis.
• Square D / Pumptrol pressure switch installation instructions, cut-in/cut-out and differential adjustment.
• NSF/ANSI 61 for well-system potable components; AWWA A100 water well standards.
• National Ground Water Association (NGWA) field guidance on private well pump and tank troubleshooting.