System guide
Well Pump Pressure Switches & Controls: How the Pump Knows When to Run
A handful of parts turn pressure into on and off: the pressure switch, the gauge, and on many submersibles a control box. Knowing which you have makes every conversation with a contractor easier.
On this page
On a conventional well system, a pressure switch starts the pump when system pressure falls to the cut-in setting and stops it at cut-out. A gauge shows you what the switch sees. Pumps with a three-wire motor also need an above-ground control box holding the starting capacitor and relay; two-wire motors have those parts built in. A constant-pressure system replaces the on/off switch with a variable-speed drive and a pressure sensor.
How a pressure switch works
Layout based on the common two-spring design. Your switch may differ — always follow the label inside its cover.
- Line terminals — power in from the breaker. Energized whenever the breaker is on, even when the pump is off.
- Hazard — removing the cover exposes live parts. Turn the breaker off and verify before touching anything.
- Contacts — close to start the pump, open to stop it. Pitted or burned contacts cause failures to start or stop.
- Range spring and nut (large) — raises or lowers cut-in and cut-out together.
- Differential spring and nut (small) — changes the cut-out only. Rarely needs adjusting.
- Diaphragm — senses system pressure.
- Pipe nipple / sensing tube — connects the switch to the tank tee. Sediment or iron can clog it.
A diaphragm at the bottom of the switch senses system pressure through a small pipe nipple on the tank tee. Springs push back against it. When pressure falls to the cut-in point, the springs win and the contacts close, starting the pump; when pressure rises to the cut-out, the diaphragm wins and the contacts open.
On the common two-nut design described in Pentair's instructions:[1]
- The range nut (large spring) moves cut-in and cut-out together — about 2½ psi per full turn. Clockwise raises the pressure.
- The differential nut (small spring) raises or lowers only the cut-out. Pentair says a 20 psi differential is best for pressure tank performance and that very few systems need the second nut adjusted.
- Pentair's limits for its pumps: never below 20 psi cut-in or above 60 psi cut-out, and the cut-out at least 5 psi below the pump's maximum (dead-head) pressure.
Live parts under the cover
The first line of Pentair's instructions is a hazardous-voltage warning: disconnect power before working on the switch.[1] The line-side terminals stay energized whenever the breaker is on, even while the pump is off. Turn the breaker off and confirm with a non-contact tester — or leave the cover on and call a pro.
Standard settings
| Setting | Cut-in | Cut-out | Tank precharge | Typical use |
|---|---|---|---|---|
| 20/40 | 20 psi | 40 psi | 18 psi | Lower-pressure systems; some jet-pump installations |
| 30/50 | 30 psi | 50 psi | 28 psi | Common default |
| 40/60 | 40 psi | 60 psi | 38 psi | Two-story homes, long runs — if the pump can reach it |
Precharge values follow the "2 psi below cut-in" rule from Amtrol and Pentair.[2][1] Deciding between the two most common settings? See 30/50 vs. 40/60.
Control boxes, two-wire and three-wire pumps
Single-phase submersible motors need extra parts to start. Franklin Electric's manual describes the two arrangements:[3]
| Two-wire motor | Three-wire motor | |
|---|---|---|
| Starting components | Inside the motor (solid-state starting switch) | In an above-ground control box: starting capacitor, starting relay and, in some sizes, overload protectors, run capacitors and contactors |
| What you see | No control box; wires run from the pressure switch to the well | A control box (usually gray) on the wall near the tank |
| Start failures | Usually mean pulling the pump | Often fixed at the control box |
| Matching rule | — | Control box must match the motor's HP and voltage; Franklin warns that the wrong box can cause motor failure |
Professional-only
Control boxes contain capacitors that can hold a dangerous charge after power is off — Pentair's manual warns capacitor voltage may be hazardous.[4] Testing or replacing capacitors, relays and overloads is work for a licensed electrician or pump installer.
Other controls you may find
- Pressure gauge
- Your main diagnostic tool. Gauges can stick or drift with age; if the reading never moves, suspect the gauge before the pump.
- Low-pressure cutoff
- A switch option with an external lever that shuts the pump off when pressure falls far below cut-in — typically because the well ran dry or a pipe broke — and stays off until reset.
- Pump protection device
- Electronic monitors such as Franklin's Pumptec-Plus watch motor power and line voltage to protect against a dry well, a waterlogged tank, high and low voltage, and more.[3]
- Surge arrestor
- Franklin's installation checklist calls for a dedicated, properly grounded surge arrestor on submersible motors.[3]
- Constant-pressure drive
- A variable-speed controller that replaces the on/off switch. See constant-pressure systems.
Guides in this section
- TroubleshootingPressure switch troubleshootingWon't start, won't stop, chattering or wrong pressures — read it from the outside.
- Comparison30/50 vs. 40/60 pressure switchMore pressure vs. more water per cycle — which setting fits your house.
- TroubleshootingWell pump won't turn onSilent pump, no water, or a breaker that trips — work from power to motor.
- Upgrade guideConstant-pressure well systemsSteady pressure from a variable-speed pump — costs, rules and trade-offs.
What control repairs cost
| Part | Installed |
|---|---|
| Pressure switch | $150–$200 |
| Pressure gauge | $150–$200 |
| Motor start capacitor | $150–$300 |
| Control box | $300–$600 |
Source: HomeGuide's well pump repair cost guide.[5] Constant-pressure systems cost $2,000–$5,000 installed by the same publisher's estimate.[6]
Sources
- Pentair. Adjusting Well Pump Pressure Switches (instruction sheet U80-129). Accessed Sept. 28, 2026.
- Amtrol. Well-X-Trol Residential Pre-Pressurized Well Tanks — Installation & Operation Instructions (WX-101 through WX-350). Accessed Sept. 28, 2026.
- Franklin Electric. Submersible Motors: Application, Installation & Maintenance (AIM) Manual, 60 Hz. Accessed Sept. 28, 2026.
- Pentair. Pro Shallow Well Jet Pumps — Installation & Operation Manual (P15001, 2023). Accessed Sept. 28, 2026.
- HomeGuide. How Much Does Well Pump Repair Cost? (article dated Aug. 6, 2025). Accessed Sept. 28, 2026.
- HomeGuide. How Much Does a Well Pump Cost To Replace or Install? (article dated Aug. 7, 2025). Accessed Sept. 28, 2026.
We cite manufacturer documentation and public agencies first. Read how we choose and check sources.