What a pressure switch does

A pressure switch is a small device that automatically starts and stops your well pump based on water pressure in your tank. When pressure drops below a set point—usually around 40 pounds per square inch (psi)—the switch flips on and the pump runs. When pressure climbs to an upper limit—typically 60 psi—the switch cuts power and the pump stops. This cycle repeats throughout the day as you use water.

Without a pressure switch, you would have to manually turn the pump on and off, and your tank would either run dry or burst from overpressure. The switch does this job automatically, which is why it is one of the most important safety devices on a well system.

Key Takeaways

  • A pressure switch monitors tank pressure and automatically starts the pump when pressure falls below the lower setpoint, usually around 40 psi.
  • The switch stops the pump when pressure reaches the upper setpoint, typically around 60 psi, creating a 20 psi operating band.
  • Inside the switch is a spring-loaded diaphragm or piston that moves when pressure changes and physically opens or closes an electrical contact.
  • If your pump runs constantly or never starts, the pressure switch is often the first thing to check because it is a common failure point.
  • Adjusting the setpoints requires a pressure gauge and an understanding of your system; incorrect adjustment can damage the pump or tank.

The two setpoints: lower and upper limits

Every pressure switch has two settings. The lower setpoint (or cut-in pressure) is the pressure at which the switch turns the pump on. The upper setpoint (or cut-out pressure) is the pressure at which it turns the pump off. The difference between them is called the differential or band.

A typical residential well system is set to cut in at 40 psi and cut out at 60 psi, giving a 20 psi band. This means the pump runs whenever tank pressure drops to 40 psi and stops once it reaches 60 psi. Some systems use 30/50 or 50/70 instead, depending on the tank size, pump capacity, and household water demand. The wider the band, the less often the pump cycles on and off.

If the band is too narrow—say, 40 to 45 psi—the pump will start and stop very frequently, which wears out the motor and the switch faster. If the band is too wide, the pressure will swing dramatically, and you may notice weak water pressure at the tap when the tank is nearly empty.

How the internal mechanism works

Inside the switch housing is a diaphragm or piston—a flexible or movable part that responds to pressure changes. One side of the diaphragm is exposed to the water pressure in your tank. The other side is connected to a spring and an electrical contact arm.

When tank pressure is low, the spring pushes the diaphragm inward, which moves the contact arm and closes an electrical circuit. This sends power to the pump motor, and the pump starts. As the pump fills the tank, pressure rises and pushes back against the diaphragm. When pressure reaches the upper setpoint, the diaphragm moves far enough to open the electrical contact, cutting power to the pump. The pump stops, and the cycle waits until pressure drops again.

The spring tension determines both setpoints. A tighter spring raises both the cut-in and cut-out pressures; a looser spring lowers them. Adjusting the spring is how technicians change the setpoints, though this is not a task for someone unfamiliar with pressure systems.

Common signs the pressure switch is failing

If your pump runs constantly without shutting off, the switch may be stuck in the on position or the upper setpoint may have drifted too high. If the pump never starts even though you have no water, the switch may be stuck in the off position or the lower setpoint may be too high. If the pump cycles on and off rapidly (more than three or four times per minute), the band may be too narrow, or the switch may be losing sensitivity.

Another sign is a loss of pressure in the tank. If the switch is not cutting off properly, the pump will overfill the tank and the pressure relief valve will vent water to drain. You may hear hissing from the relief valve or see water pooling near the tank.

Pressure switches typically last 5 to 10 years, depending on water quality and how often the pump cycles. Sediment or mineral buildup inside the switch can cause it to stick or respond slowly. If you suspect a failure, a licensed well technician can test the switch with a pressure gauge and replace it if needed.

The relationship between the switch and the pressure tank

The pressure switch works in tandem with the pressure tank, which stores water under pressure. When the pump fills the tank, air inside the tank is compressed, which raises the pressure. The switch senses this rising pressure and stops the pump. When you open a faucet, water flows out and pressure drops. The switch senses the drop and starts the pump again.

If the pressure tank is waterlogged—meaning it has lost its air charge and is full of water—the switch will cycle very rapidly because there is no air cushion to absorb the pressure change. The pump will fill the tank when ready, the pressure will spike, the switch will cut off, and then as soon as you use a small amount of water, pressure will drop and the switch will cut back on. This rapid cycling is hard on the pump and the switch. Recharging the air in the tank usually solves this problem.

Adjusting the setpoints: when and how

Adjusting a pressure switch requires a pressure gauge, a wrench, and knowledge of your system. The process involves loosening the adjustment nuts on top of the switch and turning them to change spring tension. Turning the nut clockwise raises the setpoint; counterclockwise lowers it. You must do this while the pump is running and the tank is pressurizing, and you must check the pressure with a gauge to confirm the new setpoint.

Most homeowners should not adjust the switch themselves. If the setpoints are wrong, the pump can run dry (damaging the motor) or overpressurize the tank (risking rupture). If you need to change the setpoints—for example, because you added a second bathroom and need higher pressure—call a licensed well technician. They have the tools and experience to adjust safely and verify the new settings.

One exception: if the pressure tank has lost its air charge and you have recharged it, you may need to adjust the lower setpoint slightly upward to prevent the pump from running dry during the recharge. A technician can guide you through this if needed.

Frequently Asked Questions

What pressure should my well switch be set to?

Most residential systems use 40/60 psi (cut in at 40, cut out at 60), but some use 30/50 or 50/70 depending on tank size and demand. Check your system documentation or ask your well contractor what the original setpoints were. If you have lost that information, a technician can determine the right settings for your setup.

Why does my pump run all the time?

Constant running usually means the upper setpoint is too high, the switch is stuck, or the pressure tank is waterlogged. It can also mean there is a leak in the tank or plumbing that is draining pressure faster than the pump can refill it. A technician can diagnose which by checking pressure with a gauge and listening to the pump cycle.

Can I replace a pressure switch myself?

Replacing the switch is straightforward if you are comfortable with basic plumbing: turn off the pump, drain the tank, unscrew the old switch, and screw in the new one. However, you will need to set the new switch to the correct pressure, which requires a gauge and knowledge of your system. Many homeowners hire a technician for the adjustment step to avoid getting the setpoints wrong.

How do I know if my pressure tank needs air?

If the pump cycles on and off more than three or four times per minute, the tank likely needs air. You can also check by tapping the tank with a wrench—a hollow sound means it is waterlogged, a dull thud means it has air. A technician can recharge the air using a bicycle pump or compressor.

What happens if the pressure switch fails completely?

If the switch fails and gets stuck in the off position, the pump will not start and you will have no water. If it gets stuck in the on position, the pump will run until the pressure relief valve opens and vents water, or until the motor overheats. Either way, you need a replacement switch to restore normal operation.