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.

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.