What a pressure switch does and why you adjust it
A pressure switch is the device that tells your well pump when to turn on and off. It monitors the water pressure in your tank and automatically starts the pump when pressure drops below a set point, then stops it when pressure reaches the upper limit. If your switch is set wrong, your pump will cycle too often (wearing it out faster), fail to build enough pressure for your fixtures, or stay off when you need water.
Most residential well pumps use a two-point pressure switch — typically set to turn on at 30 pounds per square inch (psi) and turn off at 50 psi. That 20-psi difference is called the differential. You may need to adjust these numbers if your water pressure feels weak, if the pump is running constantly, or if you recently replaced the tank or pump.
The adjustment itself takes about 15 minutes and requires only a screwdriver and a pressure gauge. You do not need to drain the tank or shut off power during adjustment — though you should turn off the pump before you open the switch cover.
Key Takeaways
- The pressure switch sits on top of or beside your pressure tank and has two adjustment screws under a plastic cover — one for the cut-in pressure (when the pump starts) and one for the differential (the gap between start and stop).
- Standard settings are 30 psi cut-in and 50 psi cut-out, but you should check your pump and tank manufacturer's recommendations because some systems use 40/60 or other ranges.
- You adjust the switch while the system is pressurized, using a pressure gauge attached to the tank's test port to see the current pressure in real time.
- Turning the cut-in screw clockwise raises the pressure at which the pump starts; turning it counterclockwise lowers it — the differential screw works the same way for the cut-out pressure.
- After adjustment, run the pump through a full cycle (let it build pressure, then use water until it kicks back on) and check that pressure stays within your target range.
Locate the switch and identify the adjustment screws
The pressure switch is a cylindrical or rectangular device mounted directly on the pressure tank, usually near the top. On some systems it sits on a separate bracket beside the tank. Look for a plastic or metal cover held on by one or two bolts or screws — this cover protects the electrical contacts and the adjustment mechanism underneath.
Under the cover you will see two adjustment screws. The larger one, usually labeled or positioned at the top, controls the cut-in pressure — the point where the pump turns on. The smaller screw below it controls the differential — the gap between cut-in and cut-out. Some switches label these as "Main Spring" and "Differential Spring" or straightforward mark them with arrows.
Before you touch anything, turn off power to the pump at the breaker or switch. This prevents the pump from starting unexpectedly while you work. You do not need to drain the tank or turn off water to the house.
Attach a pressure gauge and check the current settings
Locate the test port on the pressure tank — a small brass fitting that looks like a tire valve stem, usually on the side or bottom of the tank. Attach a pressure gauge (a straightforward dial gauge from any hardware store costs $10 to $20) by screwing it onto this port. Do not use excessive force; hand-tight is enough.
Turn the pump back on at the breaker. Watch the gauge as the pump runs. Note the pressure at which the pump stops — this is your current cut-out pressure. Then turn on a faucet or shower inside the house and let water run until the pump kicks back on. The pressure reading when it starts is your current cut-in pressure. Write both numbers down.
If your current settings match your target (usually 30/50 or 40/60), you may not need to adjust. If they are off by more than a few psi, proceed to the next step.
Adjust the cut-in pressure (when the pump starts)
Turn off the pump again at the breaker. Using a screwdriver that fits the larger adjustment screw, turn it clockwise to raise the cut-in pressure or counterclockwise to lower it. Make small adjustments — a quarter turn typically changes pressure by 2 to 4 psi. After each adjustment, turn the pump back on and let it build pressure, then check the gauge.
For example, if your pump is currently starting at 25 psi but you want it to start at 30 psi, turn the cut-in screw clockwise a quarter turn, run the pump, and check again. Repeat until the pump kicks on at your target pressure. This may take two or three cycles.
Once the cut-in pressure is correct, leave that screw alone. Do not adjust it again unless you need to change when the pump starts.
Adjust the differential to set the cut-out pressure
The differential screw controls how much pressure builds before the pump stops. If your cut-in is now correct but the pump is stopping too early or too late, adjust the differential screw. Clockwise raises the cut-out pressure; counterclockwise lowers it.
For a standard 30/50 system, the differential should be 20 psi — meaning the pump stops when pressure reaches 50 psi (30 + 20). If your pump is currently stopping at 45 psi, turn the differential screw clockwise a quarter turn, run a cycle, and check the gauge again.
The goal is to have the pump stop at a pressure high enough to supply your fixtures without losing water pressure during use, but not so high that the pump runs longer than necessary or the tank experiences excessive stress.
Run a full cycle and verify the settings hold
Once both screws are adjusted, turn off the pump and let the pressure bleed down completely by opening an indoor faucet until no water comes out. Then turn the pump back on and watch the gauge through a complete cycle: the pump should start at your cut-in pressure, run until it reaches your cut-out pressure, then stop. Use water inside the house and confirm the pump restarts at the cut-in pressure again.
If the pressures drift or the pump does not restart at the same point, the switch itself may be failing and may need replacement. If the settings hold steady over two or three cycles, the adjustment is complete.
Turn off the pump, remove the pressure gauge from the test port, and screw the plastic cover back onto the switch. Turn the pump back on at the breaker and return to normal operation.
Common pressure ranges for different systems
Most residential well systems use one of three standard pressure ranges. Check your pump and tank manufacturer's documentation to confirm which applies to your setup, because setting the switch outside the recommended range can damage the pump or reduce its lifespan.
| System Type | Cut-In (Start) | Cut-Out (Stop) | Differential |
|---|---|---|---|
| Standard shallow well or small tank | 30 psi | 50 psi | 20 psi |
| Larger tank or higher-demand system | 40 psi | 60 psi | 20 psi |
| Deep well or high-elevation property | 20 psi | 40 psi | 20 psi |
If you do not have the documentation, contact the pump or tank manufacturer with your model number — they can tell you the correct range in minutes. Setting the switch outside the recommended range is the most common cause of premature pump failure.
Frequently Asked Questions
What if the pump keeps running and won't shut off?
The cut-out pressure may be set too high, or the switch itself may be stuck. First, try lowering the differential screw a quarter turn to bring down the cut-out pressure. If the pump still runs continuously, the switch contacts may be worn and the switch may need replacement rather than adjustment.
Why is my water pressure weak even though the pump is running?
The cut-out pressure may be set too low, so the pump stops before building enough pressure. Raise the differential screw clockwise a quarter turn, run a cycle, and check the gauge. If pressure still feels weak at the faucet, the issue may be a clogged filter or a leak in the line rather than the switch setting.
Can I adjust the pressure switch while the pump is running?
You should turn off the pump at the breaker before opening the switch cover and adjusting the screws. However, you can turn the pump back on between adjustments to test the new settings without fully draining the tank.
How often should I check or adjust the pressure switch?
Check the settings once a year or whenever you notice a change in water pressure or pump cycling. Most switches do not drift significantly over time, but age, temperature swings, and wear on the contacts can shift the settings by a few psi over several years.
What pressure gauge should I buy?
Any basic dial pressure gauge rated for 0 to 100 psi with a 1/4-inch NPT male connection will work. You do not need a digital gauge or anything expensive — a $15 analog gauge from a hardware store is accurate enough for this job and will last for years.