What a pressure switch does and why you might adjust it
A water pump pressure switch turns your pump on and off based on the water pressure in your tank. It sits on top of the pressure tank and has two adjustment screws — one controls when the pump starts (cut-in pressure) and one controls when it stops (cut-out pressure). The difference between these two points is called the differential, usually 20 pounds per square inch (psi).
You adjust the switch when your pump runs too often, doesn't build enough pressure, or cycles on and off rapidly. Most residential systems are factory-set to start at 30 psi and stop at 50 psi, but your home's needs may be different depending on your tank size, water use, and how far water travels from the tank to your fixtures.
Before you touch anything, turn off power to the pump at the breaker. Adjusting a live switch is dangerous and unnecessary — the pump will not restart while you work.
Key Takeaways
- The larger screw (usually with a spring) adjusts the cut-in pressure where the pump starts; the smaller screw adjusts the differential between start and stop.
- Turn the large screw clockwise to raise starting pressure or counterclockwise to lower it, making quarter-turn adjustments and testing between each one.
- Most home systems work best with a 20 psi difference between cut-in and cut-out, though some tanks perform better at 30 psi.
- Check your tank's air pressure with a tire gauge before adjusting the switch — a waterlogged tank will make the switch behave unpredictably no matter how you set it.
- If the pump still cycles rapidly after adjustment, the problem is usually a leaking check valve or a tank that needs air, not the switch itself.
Locate the two adjustment screws and understand what each one does
Open the plastic or metal cover on top of the pressure switch. You will see two nuts or screws. The larger one, usually with a spring underneath it, adjusts the cut-in pressure — the point where the pump turns on. The smaller one adjusts the differential, the gap between when the pump starts and when it stops.
Some switches have only one adjustment screw that controls both settings together. Check your switch's label or manual to confirm which type you have. If you cannot find the manual, take a photo of the switch and search for the brand and model number online — most manufacturers post adjustment instructions as PDFs.
Write down the current pressure readings before you make any changes. Use a tire gauge on the pressure gauge port on your tank to see what pressure the system is holding right now. This gives you a baseline to return to if your adjustment makes things worse.
Raise or lower the cut-in pressure with the large screw
The large screw controls when the pump starts. Turn it clockwise to raise the starting pressure (the pump will wait longer before turning on) or counterclockwise to lower it (the pump will turn on sooner). Make only a quarter turn at a time.
After each quarter turn, turn the pump back on at the breaker and let the system run until the pump cycles off naturally. Watch the pressure gauge on the tank. If you raised the screw, the pump should start at a higher pressure than before. If you lowered it, the pump should start sooner. Once the pump stops, note the new starting pressure and the stopping pressure.
Most homes run best with a cut-in pressure between 30 and 40 psi. If your water pressure at the tap feels weak, raise the cut-in pressure. If the pump runs constantly or cycles every few seconds, lower the cut-in pressure — but first check that your tank's air charge is correct, because a waterlogged tank is the more common cause of rapid cycling.
Adjust the differential screw if the gap between start and stop is wrong
The smaller screw controls the differential — how many psi the pressure must drop before the pump turns back on. Most systems use a 20 psi differential, meaning if the pump starts at 30 psi, it stops at 50 psi. Some larger tanks or systems with long pipe runs work better at 30 psi differential.
Turn the small screw clockwise to increase the differential (wider gap, pump runs less often) or counterclockwise to decrease it (narrower gap, pump runs more often). Again, make quarter turns and test between each adjustment. Let the pump cycle completely — from start to stop — so you can see the new pressure range.
If you are not sure whether to widen or narrow the differential, start by leaving it where it is and adjusting only the large screw. The differential is usually correct at the factory setting, and changing it often makes things worse rather than better.
Check your tank's air pressure before blaming the switch
A pressure switch cannot work properly if the tank itself is waterlogged — meaning it has lost its air charge and filled with water instead. When this happens, the pump cycles rapidly no matter where you set the switch, because there is no air cushion to hold pressure steady.
Use a tire gauge on the air valve at the top of the tank (not the water pressure gauge). The reading should be about 2 psi lower than your cut-in pressure. If your pump starts at 30 psi, the air pressure should be around 28 psi. If the gauge reads zero or very low, the tank needs air.
To add air, turn off the pump, drain the tank completely using the drain valve at the bottom, then use an air compressor to fill the tank to the correct air pressure. This is a common fix for rapid cycling and often solves the problem without any switch adjustment.
Test the system and return to normal operation
Once you have made your adjustments, turn the pump back on and let it run through at least two full cycles — from start to stop to start again. Watch the pressure gauge and listen to the pump. It should start smoothly, build pressure steadily, and stop cleanly without stuttering or surging.
Open a faucet and run water for 30 seconds, then close it and watch the pressure gauge. The pressure should drop as water flows out, then hold steady once you close the faucet. If the pressure drops and keeps dropping even after you stop using water, you have a leak in the tank or a failed check valve, not a switch problem.
If the pump still cycles too fast, turns on and off erratically, or will not build pressure, the problem is usually not the switch. Check for leaks in the pipes, a failed check valve, or a tank that needs air before you adjust the switch again.
When to call a plumber instead of adjusting yourself
Do not adjust the switch if the pump will not turn on at all, even after you have confirmed the breaker is on and power is reaching the switch. This usually means the switch contacts are burned out or the pump itself has failed.
If you have adjusted the switch multiple times and the pump still cycles rapidly, the tank still feels waterlogged after you have added air, or water pressure at the tap remains weak even at high switch settings, a plumber should inspect the tank, check valve, and pump. These parts wear out and fail, and no switch adjustment will fix them.
If you are uncomfortable working with electrical connections or pressurized tanks, or if you have never adjusted a switch before, hiring a plumber for the first adjustment is reasonable. They can show you how the switch works and set it to the right pressure for your home's specific setup.
Frequently Asked Questions
How do I know which screw is which if the labels are worn off?
The larger screw with a spring underneath is always the cut-in adjustment. The smaller screw, usually without a spring, is the differential. If you are still unsure, turn the large screw a quarter turn clockwise, turn the pump on, and watch the pressure gauge. If the starting pressure goes up, you have the right screw. If nothing changes, you have the differential screw.
Can I adjust the switch while the pump is running?
No. Turn off power at the breaker before you open the switch cover or touch any screws. Adjusting a live switch is dangerous and can damage the switch contacts. The pump will not restart while you work, and you will have a clear view of the gauge without the pump noise.
What if I turn the screw too far and now the pump won't start?
Turn the large screw counterclockwise (lower the cut-in pressure) until the pump starts again. If it still will not start after several turns, the switch may be stuck or damaged. Return the screw to its original position, turn off power, and wait 10 minutes before trying again. If the pump still will not start, the switch likely needs replacement.
Is 20 psi differential always the right setting?
Twenty psi is the standard and works for most homes. Larger tanks or systems with long pipe runs sometimes perform better at 25 or 30 psi differential. Start at 20 psi and only change it if the pump cycles too often even after you have corrected the tank's air pressure and checked for leaks.
Why does my pump cycle on and off every few seconds even after I adjusted the switch?
Rapid cycling usually means the tank has lost its air charge, not that the switch is wrong. Check the air pressure with a tire gauge on the air valve at the top of the tank. If it reads zero or very low, drain the tank and refill it with air to 2 psi below your cut-in pressure. This fixes rapid cycling in most cases.