A well pump that clicks on and off every few seconds is short cycling, and the cause is almost always the pressure tank: a failed bladder or wrong air pre-charge has removed the cushion that lets the pump rest between draws. It's a same-week problem — hundreds of starts a day cook a motor rated for a few hundred at most. The five-minute air-charge test below names the culprit; the fix is usually $300–$800.
Why the tank matters
A pressure tank stores water under a cushion of compressed air so a few gallons can be drawn before the pump runs — that's what turns a pump's life into a few long runs a day instead of a spasm at every faucet. When the bladder tears, water fills the air space, the cushion vanishes, and the pump answers every draw personally: on, off, on, off.
The 5-minute diagnosis
- Watch the gauge while a tap runs: pressure swinging rapidly between cut-in and cut-off (e.g. 40 → 60 → 40 in seconds) = short cycling confirmed.
- Air-charge test: breaker off, drain to zero, tire gauge on the tank's air valve. Target: cut-in minus 2 psi (38 for 40/60). Water at the valve or a dull knock on the upper tank = failed bladder.
- If the charge is simply low (bladder intact, no water at valve): add air with a compressor to the target and retest — sometimes that's the whole fix.
- If cycling happens with NO water use: it's a leak, not the tank — toilets (food coloring), fixtures, then the well side. Our pump-runs-constantly guide covers that hunt.
- If the tank checks out: pressure switch (stuck/undersized differential, $25–$50) a clogged pressure-switch sensing tube, or a plugged sediment filter/restricted pipe between the pump and tank.
The fix ladder
| Cause | Fix | Typical cost |
|---|---|---|
| Low air pre-charge, bladder OK | Add air to cut-in − 2 psi | $0 |
| Failed bladder / waterlogged tank | Replace pressure tank | $300–$800 installed |
| Undersized tank for the pump | Larger tank (more drawdown) | $400–$1,000 |
| Pressure switch fault | Replace switch | $25–$50 part; $100–$250 installed |
| Check valve / drop pipe leak | Pull pump, replace valve/pipe | $300–$1,000+ |
| Ignored for months | Pump replacement | $1,200–$3,500 |
While you're deciding
If the tank has failed and the replacement is days away, minimize small draws (fill a pitcher rather than running the tap repeatedly) — every avoided start is pump life. Related symptoms live in the low-pressure diagnostic — the pulsing strong-weak pressure pattern is short cycling felt at the shower.
Frequently Asked Questions
What causes a well pump to short cycle?
Short cycling — the pump kicking on and off every few seconds — almost always means the pressure tank has lost its air cushion: a failed bladder or a wrong air pre-charge. With no cushion, the tiniest draw drops pressure to cut-in and the pump fires. Second-tier causes: a stuck pressure switch, a leak on the well side (check valve, drop pipe), a clogged pressure-switch sensing tube, or a plugged sediment filter between pump and tank.
Is short cycling bad for a well pump?
It's the fastest way to kill one. Every start is the hardest moment of a motor's life; motor makers rate small submersibles for roughly 100–300 starts a day with at least a minute of run each, and a short-cycling pump can burn through that budget in an hour, overheating windings and wearing contacts. Left alone, short cycling turns a $300–$800 pressure-tank problem into a $1,200–$3,500 pump replacement.
How do I check the pressure tank air charge?
Turn off the pump breaker, open a tap until pressure reads zero, then put a tire gauge on the tank's air valve (top). It should read 2 psi below the pump's cut-in setting — 38 psi for a 40/60 switch. Water spraying from the valve, or a dull thud when you knock on the tank's upper half, means the bladder has failed and the tank needs replacement.
Why does my pump cycle when no water is running?
Water is escaping the pressurized system somewhere: a running toilet, a leaking fixture, or — if the house is tight — a failed check valve or split drop pipe letting water drain back down the well. Cycling at rest is a leak hunt — though a waterlogged tank makes even a pinhole leak cycle rapidly, so check both. The house side first (food coloring in toilet tanks), then the well side.