Causes, ranked by likelihood
| Cause | Rough share of cases | Quick check |
|---|---|---|
| Waterlogged pressure tank (failed bladder) | ~60% | Tap the tank top to bottom — solid throughout instead of hollow-at-top means the air cushion is gone |
| Failing pressure switch | ~15% | Watch a gauge through a few cycles; erratic cut-in/cut-out points suggest the switch |
| Plumbing leaks or a running toilet | ~10% | Check for pressure drop with every fixture off; a running toilet alone can waste 200+ gallons/day |
| Failed check valve | ~8% | Water draining back into the well after each cycle empties the tank fast |
| Undersized pressure tank | ~5% | Compare tank drawdown capacity to your household's fixture count and demand |
Diagnose the tank first
Because a waterlogged tank causes the large majority of cases, start there. Tap the tank from top to bottom — a healthy tank sounds hollow at the top (air) and solid at the bottom (water). A waterlogged tank sounds solid throughout. You can also check the Schrader air valve on top of the tank: water spraying out instead of air confirms the bladder has failed.
A real case: new pump, undiagnosed short cycling
A terrylove.com user (Woody28) reported a well pump running for about 30 seconds, then sitting idle for a minute while the tank filled — on a well drilled about 19 years earlier, where "nothing has been changed other then pressure switches" and the original pump sizing was unknown. That combination — an old, unsized system with only the switch swapped over the years — is a common setup for short cycling once a tank bladder finally fails, because the tank was never the thing anyone checked.
Where the pressure switch fits in
A narrow differential (the gap between cut-in and cut-out) can mimic short cycling even with a healthy tank — if the switch is set to a differential much below roughly 20 psi, the pump will cycle more often than it should. See our adjustment guide to check your differential, and our troubleshooting guide if the switch itself seems to be misbehaving. But fix the tank first — no switch setting compensates for a fully waterlogged tank.
When to call a professional
Recharging or replacing a tank bladder, or diagnosing a check valve buried at the wellhead, is professional-grade work in most setups. If the tap test and Schrader valve check point to the tank, or if cycling continues after you've confirmed the switch and precharge are correct, that's the point to bring in a well service company rather than keep guessing.