What a pressure switch does and why you adjust it
A pressure switch is a small device mounted on your water pump's discharge line that turns the pump on and off automatically. When water pressure in your tank drops below a set point, the switch closes and the pump starts. When pressure rises above another set point, the switch opens and the pump stops. If your pump runs constantly, cycles on and off too often, or won't start at all, the pressure switch settings are usually the problem.
The switch has two adjustable screws: one controls the cut-in pressure (when the pump starts) and one controls the cut-out pressure (when it stops). The difference between these two numbers is called the differential. Most household systems use a cut-in of 30 psi and a cut-out of 50 psi, but your pump may be set differently depending on your tank size and water demand.
Before you adjust anything, turn off power to the pump at the breaker. Adjusting a live electrical device is dangerous. You will also need a pressure gauge that reads 0 to 100 psi, an adjustable wrench, and a flathead screwdriver.
Key Takeaways
- The larger screw on the pressure switch controls the cut-in pressure (pump start), and the smaller screw controls the differential (the gap between start and stop).
- Turn the pump off at the breaker before opening the switch cover or turning any screws.
- Attach a pressure gauge to the test port on your tank to read the current pressure before and after each adjustment.
- Most household systems run best with a 30 psi cut-in and 50 psi cut-out, but check your pump manual or tank label for the manufacturer's recommended range.
- After adjusting, run the pump through several cycles and watch the gauge to confirm the new pressures hold steady.
Locate the pressure switch and read the current settings
The pressure switch is a round or rectangular metal box bolted to the pump's discharge line, usually near the pressure tank. It has a cover held on by one or two bolts. Remove the cover to see the adjustment screws inside. Most switches have two screws: a larger one (usually on top) and a smaller one (usually on the side). The larger screw adjusts cut-in pressure; the smaller one adjusts the differential.
Before you turn anything, attach a pressure gauge to the test port on your pressure tank. The test port looks like a tire valve and is usually on the side or top of the tank. Screw the gauge on hand-tight. Do not use a wrench—hand pressure is enough. Now turn the pump on at the breaker and let it run until it stops on its own. Note the pressure reading when the pump shuts off. This is your current cut-out pressure. Turn the pump back on and note the pressure when it starts. This is your current cut-in pressure.
Write both numbers down. If the pump is not cycling normally—for example, if it runs constantly or won't start—the pressures are likely outside the normal range or the differential is too small.
Adjust the cut-in pressure with the large screw
The large screw controls when the pump starts. Turning it clockwise increases the cut-in pressure; turning it counterclockwise decreases it. Make small adjustments: one-quarter turn at a time. After each quarter turn, turn the pump on at the breaker, let it run until it stops, and check the gauge again.
If your pump runs constantly, the cut-in pressure is too low. Increase it by turning the large screw clockwise in quarter-turn increments until the pump stops at the pressure you want. If your pump will not start, the cut-in pressure is too high. Decrease it by turning the large screw counterclockwise until the pump starts at the right pressure.
Most household systems work well with a cut-in of 30 psi. Check your pump manual or the label on your tank for the manufacturer's recommended range. Do not set the cut-in pressure higher than the tank's rated working pressure, which is usually printed on a metal tag bolted to the tank.
Adjust the differential with the small screw
The small screw controls the differential—the pressure gap between when the pump starts and when it stops. Turning it clockwise increases the differential; turning it counterclockwise decreases it. A larger differential means the pump runs longer before stopping. A smaller differential means the pump stops sooner after starting.
Most household systems use a 20 psi differential, which means if the pump starts at 30 psi, it stops at 50 psi. If your pump cycles on and off too often (short-cycling), increase the differential by turning the small screw clockwise. If the pump runs too long before stopping, decrease the differential by turning it counterclockwise. Again, make quarter-turn adjustments and check the gauge after each one.
Do not set the cut-out pressure (cut-in plus differential) higher than the tank's rated working pressure. If your tank is rated for 60 psi and your cut-in is 30 psi, your differential cannot be more than 30 psi.
Test the pump through multiple cycles
After you have adjusted both screws, turn the pump on and let it run until it stops. Watch the gauge and note the pressure when it stops. This should match your target cut-out pressure. Now turn on a faucet or drain some water from the tank until the pump starts again. Watch the gauge and note the pressure when it starts. This should match your target cut-in pressure.
Repeat this cycle two or three more times. The pressures should be consistent each time. If the readings drift or the pump behaves erratically, the switch may be failing and may need replacement. If the pressures are stable and match your targets, close the switch cover, bolt it back on, and you are done.
Leave the pressure gauge attached to the test port for a few days so you can monitor the system. If the pressures drift or the pump starts cycling oddly, note the new readings and make another small adjustment to the appropriate screw.
Common problems and when to replace the switch
If the pump runs constantly even after you have adjusted both screws to their full range, the switch contacts may be stuck or the diaphragm inside may be ruptured. If the pump will not start no matter how far you turn the large screw counterclockwise, the switch may be faulty. In either case, the switch needs replacement, not adjustment.
A pressure switch typically costs between $40 and $150 depending on the brand and type. Replacement is straightforward: turn off power at the breaker, unscrew the old switch from the discharge line, and screw a new one on hand-tight. You do not need to drain the tank or the line. After installation, adjust the new switch using the same method described above.
If you are not comfortable working with electrical devices or pressurized water lines, hire a licensed well pump technician. The cost of a service call is usually $150 to $300, but a technician can diagnose the problem quickly and make sure the adjustment is safe.
Frequently Asked Questions
What is the difference between cut-in and cut-out pressure?
Cut-in is the pressure at which the pump starts. Cut-out is the pressure at which the pump stops. The difference between them is the differential. For example, if the pump starts at 30 psi and stops at 50 psi, the cut-in is 30 psi, the cut-out is 50 psi, and the differential is 20 psi.
Why does my pump cycle on and off every few seconds?
Short-cycling usually means the differential is too small. The pump starts, brings the pressure up quickly, and stops almost when ready. Increase the differential by turning the small screw clockwise in quarter-turn increments. A differential of 15 to 20 psi is typical for household systems.
Can I adjust the pressure switch while the pump is running?
No. Always turn off power at the breaker before opening the switch cover or turning any screws. Adjusting a live electrical device is a shock hazard. Wait at least one minute after turning off power before touching the switch.
What happens if I set the cut-out pressure too high?
If the cut-out pressure exceeds the tank's rated working pressure, you risk rupturing the tank or damaging the pump. Always check the pressure rating on your tank before adjusting. Most household tanks are rated for 60 to 80 psi.
Do I need to drain the tank before adjusting the pressure switch?
No. The pressure switch is mounted on the discharge line outside the tank, so you do not need to drain anything. straightforward turn off power, attach a pressure gauge to the test port, and adjust the screws as described.