Usually the answer is in the pressure tank and the pressure switch beside it. Here is the whole system, simulated and running. Drag the tap, or pick your symptom.
A well system cut open, simulated (not a recording; faults are sized to make each pattern visible). Drag the tap’s red-dotted handle and watch the gauge, the water in the tank and the 15-minute pressure trace. Amber dashes: the switch’s cut-in and cut-out. Red bars: pump running. Below 0 psi, the air charge slider removes air a gauge cannot show (an empty waterlogged tank still reads 0).
A well pump should run for a minute or more, then rest for minutes. If yours clicks on and off every few seconds, the usual cause is a pressure tank that has lost its air charge: the tank is full of water but has almost nothing left to push it back out, so every glass of water drops the pressure to the switch’s cut-in and starts the pump again [1][2]. The other suspects are a tank too small for the pump, a pressure switch set wrong, a leaking check valve, or a pump that can no longer reach its cut-out.
Figure 1 The same simulated system, pinned while you read. Each step switches it to one state; drag the tap or change anything to take over, and use Return to the story to hand back. Simulated, sized to make each pattern visible; not a recording.#
At the tap: steady pressure that drifts gently between 40 and 60 psi. On the gauge: the needle falls slowly while water runs, the switch clicks, and the pump runs for a minute or more to bring it back to cut-out. With one tap at 2 gpm the pump runs about a minute and a half and rests about four.
Why: the 32-gallon tank’s air charge, squeezed between cut-in and cut-out, holds about 8 gallons it can give back: the amber dimension line beside the tank. That volume, the drawdown, sets how long each run and each rest last. This slow 40↔60 swing is normal.
At the tap: the pump clicks on and off every few seconds whenever water runs. On the gauge: the needle sweeps from cut-in to cut-out and back within seconds.
Why: air is the spring. A fixed amount of air obeys Boyle’s law [3], so with little air left the tank reaches both switch pressures with almost no change in volume; the drawdown shrinks to about half a gallon and the starts run past a hundred an hour. Air leaks out slowly through the valve, or much faster through a failed bladder.
Also: a tank far too small for the pump, or a clogged filter or other blockage on the pump’s outlet side, can cause very rapid cycling [4]. A tank that has lost air may be corroded inside; tank makers say it must not be re-pressurized and leave precharge work to licensed professionals [1].
At the tap: spurts of air, then the pump starts to cycle faster and faster. On the gauge: runs that start long and get shorter, minute by minute, until the pattern matches step 2.
Why: water floods the air side, and the air that should stay sealed leaves with the water; as it goes, the drawdown shrinks and the tank waterlogs [2].
Also: air at the taps often comes from the well side instead: a water level drawn down to the pump, a leaking drop pipe, a check valve that drains back, or an air-volume control on an older plain steel tank [2]. Spitting is a clue, not a diagnosis.
4. Undersized tank: short runs while one tap runs§
At the tap: pressure that rises and falls every minute or so while one shower runs. On the gauge: the normal 40↔60 swing of step 1, coming round much faster, with runs of seconds.
Why: a healthy 7.4-gallon tank gives back under 2 gallons, so the same pump refills it in seconds. Franklin Electric asks for at least one minute of running per start [5], and Amtrol sizes tanks on one minute for pumps up to ¾ hp [6]; this tank cannot give that. The calculator works out the tank your pump needs.
Also: a larger tank that has lost part of its air charge looks the same.
At the tap: weak pressure everywhere, never above 40 psi. On the gauge: the needle sits near 38 to 40, then dips to cut-in before the pump starts.
Why: at 20/40 the most the switch ever allows is 40 psi. The tank still carries a 38 psi precharge, so it is empty before the pump starts: the precharge belongs 2 psi below the cut-in, set with the tank drained [1][7].
Also: low pressure everywhere also comes from a clogged sediment or treatment filter, a worn pump, a well that cannot keep up, or rusted or undersized pipe [8]. If the gauge reads normal but the taps are weak, look downstream at filters and pipes.
6. Leaking check valve: starts with nobody using water§
At the tap: nothing is running, yet the pump starts now and then. On the gauge: a slow fall from cut-out to cut-in with every tap shut, then a short refill.
Why: the check valve is what holds the system’s pressure when the pump stops [5]. If it leaks, water drains back down the well and the pressure goes with it.
Also: a slow leak in the house, such as a toilet that keeps refilling, does the same [4]. Check the house first. Check valves sit at or near the pump, with more in the drop pipe on deep wells; only some installations, those with a well seal or well pit, have one near the tank [5][9]. Finding and replacing a leaking one is a job for a pump professional.
At the tap: water, but the pump never goes quiet. On the gauge: here the needle is stuck a little below cut-out, about 44 psi, and the switch never opens.
Why: a pump has a maximum pressure it can make, which falls as it wears or as the well’s water level drops. If that maximum is below the cut-out, the switch never opens. Turning the cut-out down hides the cause.
Also, and read the gauge: stuck below cut-out points to the pump, the well, running water or a leak. At or above the usual cut-out points to a cut-out set too high, a clogged switch sensing port or a switch that fails to stop the pump, and a pump that keeps running creates a dangerous over-pressure condition [4]. Turn the pump off at the breaker and call a licensed well or pump professional.
The tour above simulates one mechanism for each symptom. Real faults overlap, so here is the longer list. It is a guide to describing the problem, not a diagnosis; a licensed well or pump professional confirms the cause before parts are replaced.
Rapid clicking, every few seconds. Most often a waterlogged tank or a precharge that is too low; very rapid cycling can also come from a clogged water filter or another blockage on the pump’s outlet side [4].
The pump restarts every minute or so while one tap runs. A tank too small for the pump, or one that has lost part of its charge. A slow swing from cut-in to cut-out every few minutes is how a healthy on/off system works.
Taps spit air. A burst bladder releases air, and the tank then waterlogs; but air at the taps also comes from the well side: a water level drawn down to the pump, a leak in the drop pipe, a check valve that lets water drain back, or an air-volume control on an older tank [2].
The pump never shuts off. With the gauge stuck below cut-out: running water or a leak, or a damaged pump that cannot reach the cut-out. With the gauge at or above the usual cut-out: a cut-out set too high, a clogged switch sensing port or a switch that fails to stop the pump, and a pump that keeps running creates a dangerous over-pressure condition [4][1]. That case calls for the breaker and a professional.
Low pressure at every tap. A switch set low, a clogged sediment or treatment filter, a worn pump, a well that cannot keep up, or rusted or undersized supply pipe [8].
The pump starts with nobody using water. A slow leak such as a toilet that keeps refilling, or a leaky check valve in the well piping [4].
Safety first. The pressure switch carries line voltage. Never open its cover with the power on: turn the pump off at the breaker first, and if you are unsure, call a licensed well or pump professional. Tank makers warn that a tank which has lost air may be corroded inside and must not be re-pressurized; they reserve precharge checks and adjustments for licensed professionals [1]. Licensing and codes vary by state and county; in Wisconsin, for example, only licensed pump installers may install or replace pumps and pressure tanks [10]. This page explains how the system works so you can describe the problem accurately; it is not a repair procedure.
A submersible pump either runs at full speed or stops. Your taps, meanwhile, want any flow from a trickle to a shower. The pressure tank sits between them. Inside a modern tank a rubber bladder or diaphragm separates water from a sealed charge of air. As the pump pushes water in, the air is squeezed and its pressure rises; when you open a tap, the squeezed air pushes the water back out [1].
The pressure switch watches that pressure. When it falls to the cut-in setting, its contacts close and the pump starts; when it climbs to the cut-out, they open and the pump stops. Common factory settings are 20/40, 30/50 and 40/60 psi, and the gap between the two numbers is the differential[11]. The water the tank gives back between cut-out and cut-in is its drawdown, and the whole story of cycling is the story of that one number.
Each pump start pulls a surge of current and heats the motor. Franklin Electric’s motor manual warns that excessive cycling damages control components, motor splines and bearings, and overheats the motor; it asks for at least one minute of running per start and lists a maximum of 300 starts a day for its smaller encapsulated motors [5]. Tank makers size tanks around the same rule: Amtrol’s sizing table assumes a one-minute run for pumps up to ¾ hp and two minutes above [6].
The run time is easy to estimate. If the pump delivers Q gallons per minute and the house uses d, the tank fills its drawdown in drawdown ÷ (Q − d) minutes and empties it in drawdown ÷ d. A 7 gpm pump with an 8 gal drawdown runs over a minute even with every tap shut. Shrink the drawdown to half a gallon and the same pump runs four seconds. In the simulation at the top, set the tank size slider to 7 gallons and watch the count of starts per hour climb. You can run your own numbers in the pressure tank calculator.
“Waterlogged” sounds like the tank has too much water in it. The trouble is the opposite: it has too little air. Air is the spring. A fixed amount of air at a fixed temperature obeys Boyle’s law: halve its volume and its absolute pressure doubles [3]. A tank with a full charge of air changes pressure slowly as water comes and goes, so many gallons pass between cut-out and cut-in. A tank with only a little air reaches the same pressures with a tiny change in volume, and the drawdown collapses to pints.
Air leaves in two ways. It can leak slowly through the tank’s air valve, and the precharge sinks over the years. Or the bladder or diaphragm ruptures and water floods the air side; the air then escapes with the water, which is why a failing tank often announces itself with taps that spit air before the rapid cycling starts [2]. Amtrol’s manual treats a falling cycle time or precharge as a warning that the tank may be corroded inside and says such a tank must not be pumped back up [1]. Replacing a tank is a job for a licensed installer in many places [10].
The sign on the gauge is the one the simulation shows: the pressure falls from cut-out to cut-in after very little water has run. Step 2 of the tour shows it: the tank drawing is almost all blue, and the dimension line beside it, the drawdown, has shrunk to a fraction of a gallon.
The precharge is the air pressure in the tank when it holds no water. Amtrol and Goulds both tell installers to set it 2 psi below the switch’s cut-in, measured with the tank drained and the pump off: 38 psi for a 40/60 switch [1][7]. Measuring it with water in the tank reads the water pressure, not the air charge, which is why the check needs the system drained.
The 2 psi is a compromise you can see in the physics. With the precharge at cut-in the tank gives back the most water, and its last drop leaves exactly as the pump starts. A little below, a small cushion of water is still in the tank at cut-in, so the taps never see the pressure fall faster than the switch can react. Too far below and part of the air’s spring is wasted. Precharge set above cut-in is worse: the tank runs empty while the pressure is still above cut-in, the pressure then drops straight to cut-in, and the taps sag on every cycle. Choose “Pressure is low at every tap” above to see that case. The essay on how the tank stores water works through all of it with Boyle’s law.
Pressure switch settings and a pump that will not stop§
The switch has two settings. The cut-in is the pressure at which its contacts close and start the pump; the cut-out is the pressure at which they open; the gap between them is the differential. On the common Square D Pumptrol switch, a large range nut sets the cut-in and a smaller differential nut sets the cut-out, and with it the differential [12]; the adjustable differential is roughly 15 to 30 psi [11]. Some switches add a low-pressure cut-off that stops the pump if pressure falls about 10 psi below cut-in, as it would if the well ran dry or a line broke [11]. Any change is made with the power off at the breaker, and by a licensed well or pump professional if you are unsure.
Raising the switch does not raise what the pump can deliver. A pump has a maximum pressure it can make, which drops as it wears or as the well’s water level falls. If that maximum is below the cut-out, the switch never opens and the pump runs until something fails. Turning the cut-out down may stop the running, but it hides the cause. If the setting changes, the tank’s precharge must change to match (2 psi below the new cut-in), and with the tank drained.
A pump that starts when no water is being used is the mirror image: something is letting pressure out. Either a leak in the house (a toilet that keeps refilling, for example) or a check valve that no longer holds, letting water drain back down the well; Franklin requires at least one positive-sealing check valve because it is what holds the system’s pressure when the pump stops [5]. Step 6 of the tour shows the pressure falling with the taps shut.
Adjusting the switch. Any adjustment happens inside a box with live terminals. Power off at the breaker first, confirm it is off, and if you are unsure, have a licensed well or pump professional do it. Local codes and licensing rules vary. Nothing here guarantees that a given setting, tank size or pump suits your system.
The essay How a pressure tank stores water in squeezed air explains why a 20-gallon tank holds only about 5 gallons you can use, how the precharge sets that number, and why constant-pressure pumps need only a small tank. The drawdown and run-time calculator works out drawdown, run time and starts per hour for your own tank, switch and pump.
Physics of Buildings explains the systems inside homes and commercial buildings through their physics. This is its first piece. Every model is checked by an independent verifier against the sources cited; see about this pilot and the sources.
Amtrol (2019). Well-X-Trol Installation and Operation Instructions, 9015-868 MC10185 (06/19). Amtrol, West Warwick, RI. manufacturer manualHow a well tank works (air above the diaphragm compressed as water enters); set precharge 2 psig below cut-in (38 psig for 40/60); adjust only with the tank drained and the system off, at ambient temperature; explosion hazard warnings; only licensed professionals should check or re-charge; licensed professional inspection yearly.
Friedman, D. (InspectApedia) (2024). Diagnose and Repair Air Discharge at Faucets and Fixtures. InspectApedia. reference websiteCauses of air at the taps on a private well: falling well water level, a leak in the drop pipe, a failed air-volume control, a burst bladder (the tank then waterlogs and the pump short-cycles), a check valve that lets water drain back. Year approximate (page undated; read 2026-11-10).
Friedman, D. (InspectApedia) (2024). Water pump won't start, won't stop, or short cycles (diagnostic table 1 of 3). InspectApedia. reference websitePump will not shut off: water running, damaged pump cannot reach cut-off, cut-off set too high, clogged pressure-switch sensor port; a pump that does not turn off creates a dangerous over-pressure condition. Short cycling: waterlogged tank most common, too little precharge; very rapid cycling can be a clogged water filter or blockage on the pump's outlet side. Pump starts with no use: slow leak (running toilet), leaky check or foot valve. Year approximate (undated; newest reader note 2024; read 2026-11-10).
Franklin Electric (2026). AIM Manual: 60 Hz Submersible Systems, Application · Installation · Maintenance, 2026 edition. Franklin Electric Co., Fort Wayne, IN (copy hosted by the Nebraska Department of Water, Energy, and Environment). manufacturer manualp. 4 Frequency of Starts: excessive cycling damages control components, splines, bearings and windings; run motors at least one minute; maximum starts per 24 h (300 for encapsulated motors up to 0.75 hp); p. 7 check valves hold pressure when the pump stops; VFD section: small tank, 10–20% of pump output per minute, max 200 starts/24 h.
Xylem / Goulds Water Technology (2025). HYDRO-PRO Tanks: Cross Reference and Sizing Guide, CRSGTANK R2. Xylem Inc., Seneca Falls, NY. manufacturer data sheetSizing for one-minute ('adequate') and two-minute ('recommended') pump run times at 20/40, 30/50 and 40/60; 'Precharge at 2 lbs. below cut-in setting of pressure switch.' Revision R2, dated 3/2025 in the footer.
Friedman, D. (InspectApedia) (2024). Diagnose and Repair Poor Water Pressure / Lost Well Water Pressure. InspectApedia. reference websitePoor pressure from pump, tank or control-switch problems; low well yield; rust-clogged steel supply piping; small-diameter piping limits flow; a clogged water filter reduces pressure. Year approximate (undated; read 2026-11-10).
Xylem / Goulds Water Technology (2025). 4" Submersible Pumps Quick Guide, IM453 Rev 2. Xylem Inc.. manufacturer manualCheck valve for every 200 ft of vertical pipe; some installers add one on the discharge even with a built-in valve; with a pitless adapter the top check valve should be below the pitless, not at the tank; with well seals or well pits it is allowable to locate the top check valve near the tank. Footer IM453_Rev 2_2025-07.
Wisconsin Department of Natural Resources (2021). You and Your Well (PUB-DG-002). Wisconsin DNR, Drinking and Groundwater program. state guidanceIn Wisconsin only persons with a current pump installer license may install and replace pumps, pitless adapters, piping and pressure tanks. Year approximate (no date printed).
Square D by Schneider Electric (2011). Pumptrol Water Pump and Air Compressor Pressure Switches (catalog pages, Class 9013 Type FSG). Schneider Electric. manufacturer catalogStandard settings 20/40, 30/50, 40/60 psig; FSG2 cut-in range 20–65 psig, adjustable differential about 15–30 psig; 'Differential: the difference between cut-in and cut-out pressure'; low-pressure cut-off option opens at about 10 psig below cut-in to stop the pump if it runs dry or a line breaks.
Schneider Electric (2007). How do you adjust the settings on a 9013FSG switch? (FAQ FA121330). Schneider Electric. manufacturer FAQThe large range nut sets cut-in (and moves cut-out with it); the small differential nut sets cut-out only. Published 2007, modified 2026.