Why does my well pump turn on and off so fast?

What the pump is actually doing

A well system that's working right runs in long, lazy cycles. You open a tap, pressure falls to the cut-in point, the switch closes, the pump runs for a minute or two while it pushes water into the tank and out to the faucet, pressure climbs to cut-out, and the pump shuts off. Then the tank feeds the house alone until pressure drops again. On a typical 40/60 setting, that's the whole rhythm.

Short cycling breaks that rhythm into pieces. The pump kicks on, runs three or four seconds, shuts off, and a few seconds later it does it again. From the basement you hear the pressure switch clicking like a metronome and the gauge needle sweeping back and forth across its whole range. At a faucet, the pressure surges and sags while you're standing there with your hands under the water.

It's worth separating this from a pump that runs and never stops. Constant running points at a well that can't keep up, a leak, or a pump that's lost its ability to build pressure. Short cycling is the opposite problem. The pump builds pressure just fine. It's that there's nowhere to put the water, so the system hits cut-out almost immediately and starts over.

This is an emergency that doesn't look like one. Nothing's flooding and you still have water. But the clock is running on the most expensive part of your water system, and the part that's failing is one of the cheapest.

Nine times out of ten it's the tank

A pressure tank isn't a water storage tank. It's an air spring. Inside a modern tank there's a rubber bladder or diaphragm with water on one side and a charge of compressed air on the other. When the pump runs, water pushes in and squeezes the air. When you open a faucet, that compressed air pushes the water back out. The volume of water a tank can deliver between cut-in and cut-out is called drawdown, and drawdown is the entire reason the tank exists.

Take the air away and the tank stops working. Water doesn't compress. A tank full of water with no air cushion has a drawdown measured in ounces, not gallons. So the pump fills that last cup of space, hits 60 psi, shuts off, you run the kitchen sink for three seconds, pressure falls to 40, and the pump starts again. Nothing is wrong with the pump. It's doing exactly what it's told, over and over, because the buffer between it and your faucet is gone.

The numbers make it obvious. A common 86 gallon bladder tank at a 40/60 setting gives you somewhere around 20 to 25 gallons of drawdown when it's charged properly. That's enough for the pump to run a real cycle. That same tank waterlogged gives you a fraction of a gallon, and the pump cycles thirty or forty times during one shower.

Tanks lose their air two ways. On a bladder tank the rubber tears or the air valve leaks, and once the bladder's torn the air and water mix. On an older galvanized tank with no bladder at all, the air simply dissolves into the water over time and leaves with it, which is why those tanks need to be recharged periodically and modern ones don't.

Check the tank yourself with a tire gauge

You need a tire pressure gauge and five minutes. Start by shutting the pump off at the breaker, not just at a switch. Then open the lowest faucet in the house, a basement laundry tub or an outside hose bib, and let it run until the water stops completely and the gauge on the tank reads zero. You have to get every bit of water pressure out, because any pressure left in the tank will read on top of the air charge and give you a number that means nothing.

Now find the Schrader valve on the tank. It's the same valve stem you'd find on a car tire, and on most tanks it's under a plastic cap on the very top. Unscrew the cap and put the tire gauge on it exactly the way you'd check a tire.

The reading should be 2 psi below your pressure switch cut-in. On a 40/60 switch, you want 38 psi. On a 30/50 switch, 28 psi. That 2 psi difference is what lets the tank push the last of its water out before the pump restarts, and it's the setting that gives you full drawdown.

A reading of zero or close to it means the tank has lost its charge and that's your short cycling. A reading of 20 when it should be 38 means the same thing, less severely. And if water comes out of the valve stem instead of air, stop there. The bladder is ruptured, the tank is finished, and no amount of pumping air into it will bring it back. That tank gets replaced.

The other causes worth ruling out

A clogged pressure switch tube is the one homeowners never think of. The switch senses system pressure through a small tube or nipple, often a quarter inch, that connects it to the tank tee. In iron-heavy water that passage packs up with rust and scale until the switch is reading a delayed, jumpy version of what the system is actually doing. It'll snap open and closed on tiny swings. A switch tube that's leaking does something similar, bleeding off pressure so the switch never sees a stable reading. Clearing or replacing that tube is a cheap fix when it's the culprit.

A leak on the discharge side makes a healthy system cycle. Anywhere water escapes between the pump and your fixtures counts: a cracked line running out to a barn or a hydrant, a toilet flapper passing water all night, an irrigation zone valve that isn't sealing. Pressure bleeds down, the switch calls for the pump, the pump tops it off, and around it goes. The tell is that it cycles when nobody's using water. Shut off the main valve to the house and see if the cycling stops. If it does, the leak is inside. If it keeps going, it's between the well and that valve.

A failing check valve lets the water column in the drop pipe fall back down the well after the pump shuts off. The pump starts against a partly empty pipe, pressure spikes and collapses, and you get a cycling pattern that can look a lot like a dead tank. On a deep well with more than one check valve in the string, one bad valve is enough to do it.

Last, a pressure switch with too narrow a differential, or one that's been adjusted by somebody chasing a pressure complaint, will cycle a pump on a perfectly good tank. A standard switch is built for a 20 psi spread. Squeeze that down to 10 and you've cut your drawdown in half.

Why this kills pumps

Motors don't die of running. They die of starting. A submersible motor draws roughly six times its running current at the instant it starts, and all that inrush turns into heat in the windings and mechanical shock through the thrust bearing and the shaft. The motor is built to absorb that a set number of times. Run hours barely matter by comparison. A pump that runs four hours straight every day will outlive one that runs six minutes a day in four hundred separate starts.

That's why the tank sizing rule in this trade is simple: the pump should run at least one full minute per cycle. Size the tank so the drawdown between cut-in and cut-out takes a minute or more to fill at the pump's gallons per minute, and the motor gets time to cool and settle between starts. That rule is why a 5 gallon tank on a 10 gpm pump is a mistake even when it holds pressure.

Short cycling throws that out entirely. A pump cycling every eight seconds can rack up hundreds of starts in a day, more than it would see in a normal month. The heat has nowhere to go because the pump never runs long enough to move cooling water past the motor. The pressure switch contacts pit and burn from the constant arcing. Control box components on a three-wire setup cook. A pump that had ten good years left in it can be finished in a week of this.

The cheapest emergency in the business

Here's the arithmetic that should get you off the fence. A new 40 gallon nominal bladder tank is a modest part, and most straightforward swaps are a same-day job with a new tank tee, switch and fittings. It's a couple of hours in the basement and nobody touches the well.

A submersible pump pulled from 400 feet is a different animal. That's a truck with a hoist, four hundred feet of pipe and wire coming up out of the ground, a new pump, and often new pipe and wire on the way back down because it's foolish to send old pipe back into a hole you just opened. That is the expensive end, and depth, horsepower and what the crew finds decide where you land. If the well's over 500 feet, which plenty are around here, it goes up from there.

So a tank you replace this week is a few hundred dollars. The same tank ignored for a month can turn into a pump job that costs five to ten times as much. There is no other failure on a well system where acting early saves you that ratio.

Call 973-853-1550. Tell us how fast it's cycling, what the gauge reads at cut-in and cut-out, and whether you got air or water at the valve stem on top of the tank. That's enough for us to know what's going on the truck before we leave the shop, and we can be there today on most short cycling calls.