Well Pump Short Cycling — Causes & Fixes

What Is Short Cycling?

Short cycling is when your well pump turns on and off repeatedly in rapid succession — sometimes every 2–10 seconds. Each motor start draws 3–5x normal running amperage, overheating the windings and wearing bearings at an accelerated rate. A pump that short cycles for weeks instead of months can fail in a fraction of its normal lifespan.

Cause 1: Waterlogged Pressure Tank (Most Common)

The bladder in your pressure tank has failed. The tank is completely full of water with no air cushion. Every drop of water used triggers the pump because there is no stored pressure to draw from.

Test: Press the Schrader valve with pump off and pressure at zero. Water = failed bladder. Replace the tank.

Cause 2: Incorrect Pre-Charge Pressure

Even with an intact bladder, a tank with wrong pre-charge pressure delivers poor storage. Pre-charge must be 2 PSI below cut-in (28 PSI for 30/50, 38 PSI for 40/60). Check and adjust with a tire gauge.

Cause 3: Undersized Pressure Tank

A tank too small for your pump GPM stores insufficient water per cycle, causing rapid cycling even when functioning correctly. Use our calculator to verify your tank is properly sized for your pump.

Cause 4: Pressure Switch Differential Too Narrow

Standard switches have a 20 PSI differential (30/50 or 40/60). A switch with less than 15 PSI between cut-in and cut-out will cycle more rapidly than normal. Replace with a standard differential switch.

How to Diagnose Short Cycling Step-by-Step

Work through causes in this order — it goes from fastest-to-check to most involved:

1. Listen and time it. Time the interval between pump starts with a stopwatch. Under 15 seconds between starts at moderate flow (a single faucet running) points hard at a waterlogged tank or a badly undersized one.
2. Check the Schrader valve first. With the pump off and system pressure released to zero, press the valve stem. Air only = bladder is fine, move to pre-charge. Water spitting out = bladder has failed, the tank needs replacement, not just re-charging.
3. Verify pre-charge with the pump off and tank empty of pressure. Use an actual tire gauge, not a guess. If it reads more than 2 PSI off the target for your switch setting, adjust it before assuming the tank itself is bad.
4. Recheck timing after adjusting pre-charge. If cycling is still fast, the tank is very likely undersized for your pump's flow rate — run the sizing calculator with your pump's actual GPM, not an estimate.
5. Only then check the switch. Pressure switches fail less often than tanks, so rule out the tank first. If cut-in/cut-out differential measures under 15 PSI with a gauge, replace the switch.

Short Cycling vs. Normal Cycling — What to Expect

A correctly sized system with a healthy tank should run for at least 1 minute per cycle under typical single-fixture draw, often 2 minutes or more on larger tanks. If you're seeing cycles well under a minute during normal use — not during unusually high flow like filling a pool or running two showers at once — that's abnormal, not just "on the fast side."

What Short Cycling Actually Costs You If Ignored

Every motor start is the highest-stress moment in a pump's operating life — inrush current alone can hit 3-5x running amps for a fraction of a second, and that repeated thermal and mechanical stress adds up fast. A pump rated for a normal 10-15 year service life can fail in under a year of continuous short cycling. Replacing a submersible well pump typically runs $800-$2,500 installed depending on depth and horsepower — considerably more than the $150-$400 a new pressure tank or pressure switch costs. Catching short cycling early is one of the cheapest repairs you'll make on a well system.

Keeping It From Coming Back

Once you've fixed the cause, check pre-charge pressure annually — bladders lose a small amount of air pressure over time even when healthy, and pre-charge drift is the most common reason short cycling quietly returns 2-3 years after a repair. Check it when the system is depressurized during any other well maintenance, and keep a note of your target PSI (2 PSI below cut-in) somewhere accessible, like taped to the tank itself.