How short is too short?
Franklin Electric, a major submersible well motor maker, says its motors should run at least one minute per start to get rid of the heat built up by the starting current, and that excessive cycling shortens the life of control components and can cause motor spline damage, bearing damage or overheating. Its manual also caps the number of starts a day:
| Motor size | Single-phase | Three-phase |
|---|---|---|
| Up to 0.75 HP | 300 | 300 |
| 1 – 5.5 HP | 100 | 300 |
| 7.5 – 30 HP | 50 | 100 (200 with a properly configured reduced-voltage starter or VFD) |
The same manual's installation record adds a stricter rule for three-phase motors above 7.5 HP in a vertical potable water well: no more than 100 starts in 24 hours, with each start including at least 3 minutes on and 10 minutes off.
Two more limits in the manual narrow the table: 6-inch and larger encapsulated motors without a reduced-voltage starter or VFD need at least 15 minutes between starts or starting attempts, and for motors not mounted vertically shaft-up, Franklin says to keep starts under 10 per 24 hours (with at least 20 minutes between starts or starting attempts for 6- and 8-inch motors). For three-phase motors on a variable frequency drive, the manual recommends a maximum of 200 starts per 24 hours in all cases.
Franklin's advice is to choose the pump size, tank size and controls to keep starts per day as low as possible. A pump that shuts off after less than a minute of running is below Franklin's minimum for its motors; if your motor is another brand, check that maker's manual for its own limits.
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.
Franklin Electric's checklist for "motor starts too often"
Franklin Electric's system troubleshooting table lists four possible causes for a motor that "starts too often":
| Possible cause | Franklin's check | Franklin's corrective action |
|---|---|---|
| Pressure switch | Check the setting on the pressure switch and examine it for defects | Reset the limit or replace the switch |
| Check valve stuck open | A damaged or defective check valve will not hold pressure | Replace if defective |
| Waterlogged tank | Check the tank's air charge | Clean or replace |
| Leak in system | Check the system for leaks | Replace damaged pipes or repair leaks |
For the air-charge check, Amtrol's Well-X-Trol manual says the precharge should be 2 psi below the switch's cut-in pressure (28 psi on a 30/50 switch), measured with the pump powered off and the tank drained of water. Water spraying from the air valve instead of air means the bladder has failed (see the tank check above).
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.