Short cycling, a pump that turns on and off every few seconds while water runs, almost always comes from the pressure tank: it has lost its air charge, its bladder has torn, or it is too small for the pump. Leaks, a leaking check valve and a clogged pressure switch port can cause it too. Every start heats the motor and wears the switch, so it is worth fixing quickly.
Key points
- Tap the tank: solid all the way up means waterlogged.
- Air charge should be about 2 psi under cut-in, set with the tank empty.
- Water at the air valve means a torn bladder.
- Short cycling shortens pump and switch life.
Wellborne fixes short-cycling well systems across Suffolk and the surrounding area, and in most cases the fix is at the tank, not the pump. Catching it early is what keeps a healthy pump healthy.
What short cycling looks and sounds like
Open a tap and listen. A healthy system runs the pump steadily for a minute or more while the tap runs. A short-cycling one clicks on, runs a few seconds, clicks off, and repeats. The pressure gauge swings quickly between cut-in and cut-out, and showers pulse strong and weak.
Why the tank is usually the cause
A bladder tank stores water against a cushion of compressed air. That stored water, the drawdown, is what lets the pump run for a reasonable time and then rest. When the tank fails, the drawdown collapses and the pump has to restart almost as soon as it stops.
- Lost air charge. Tanks lose air slowly over years. With too little air, the bladder holds little water.
- Torn bladder or diaphragm. Water fills the whole tank and there is no cushion at all. The tank is waterlogged.
- Undersized tank. A tank too small for the pump’s flow, often after a larger pump has been fitted, gives too little drawdown even when healthy.
Quick checks you can do
- Tap the tank. Knock on the side from top to bottom. A healthy tank sounds hollow above the waterline; a waterlogged tank sounds solid all the way up.
- Check the air valve. On top of the tank, under a cap, is a tire-style valve. Briefly press the core. Air means the bladder is probably intact; water means it has failed.
- Watch a cycle. Note how many seconds the pump runs with one tap open.
Do not open the pressure switch, which carries line voltage.
Setting the air charge correctly
The air charge is read and set with the pump off and the tank drained of water, so the gauge reads only the air. It should sit about 2 psi below the pressure switch’s cut-in: 38 psi for a 40/60 switch, 28 psi for 30/50. A tank charged with water pressure still on it reads falsely high. If the tank holds its charge after setting, the problem is solved. If it loses it again within weeks, the bladder or the tank’s air valve is leaking, and the tank is replaced.
Other causes
If the tank is healthy and the pump still cycles:
- A small leak or a dripping fixture lets pressure fall to cut-in between uses, so the pump cycles even with nothing on.
- A leaking check valve lets the water column drain back, dropping pressure.
- A clogged pressure switch port reads pressure late, making the switch chatter.
- A pump set too close to the water level may cycle as it draws air and loses pressure.
After a pump replacement
A newly replaced pump that starts short cycling usually means the tank was not checked or was left too small for the new pump’s flow, or the switch range was changed without adjusting the tank charge. It is worth catching in the first days, before it shortens the new pump’s life.
Why it matters
Each start sends several times the running current through the motor and the switch contacts. A pump that starts every few seconds can make thousands of extra starts a week, heating its windings and burning the switch. On deep Suffolk wells, where pulling a pump is a big job, a cheap tank fix is the best protection a pump gets. A constant pressure system is another way to end cycling on systems where space or demand makes a large tank impractical. To get it checked, call (757) 919-1972.