How to Adjust a Well Pump Pressure Switch (Safely)

Short answer

On a standard two-nut pressure switch, the large (range) nut raises or lowers cut-in and cut-out together — clockwise for higher pressure. The small (differential) nut changes only the cut-out and rarely needs touching. Square D's bulletin gives the turns: about 3½ turns clockwise to go from 20/40 to 30/50 or from 30/50 to 40/60.^[1] The breaker must be off before the cover is removed, and the tank's air precharge has to be reset to 2 psi below the new cut-in.

Is this a job for you?

Under the switch cover are bare terminals at line voltage. They are live whenever the breaker is on — whether or not the pump is running. Pentair's instructions open with a hazardous-voltage warning to disconnect power before working on the switch.^[2]

We'd only suggest doing this yourself if all three are true: you can identify and switch off the correct breaker, you can confirm the power is off with a tester, and you know your pump can reach the higher pressure. If not, have it done by whoever services your tank — the precharge has to be changed in the same visit anyway.

Before you change anything

Measure what you have. Watch the gauge through a pump cycle and note the real cut-in and cut-out. Square D's first adjustment step is the same: monitor the gauge to find where the switch turns on and off.^[1]
Decide what you actually want. Usually that's moving the whole range up (30/50 → 40/60). Compare the trade-offs in 30/50 vs. 40/60.
Check the limits. Pentair says its switches should never be adjusted to cut in below 20 psi or cut out above 60 psi, and that the cut-out should always be at least 5 psi below the pump's dead-head (maximum) pressure.^[2] If the pump can't reach the new cut-out, it will run without shutting off.
Read the label inside the cover once it's off. Your switch's range and instructions are printed there, and they take priority over any general guide.

Which nut does what

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.

Pressure switch adjustment nuts
Nut	Changes	Direction
Range nut (large spring)	Cut-in and cut-out together; the differential stays the same	Clockwise = higher pressure
Differential nut (small spring)	Cut-out only; cut-in doesn't change	Clockwise = higher cut-out

Both Square D and Pentair describe the nuts this way.^[1]^[2] Pentair adds that the standard 20 psi differential is best for pressure tank performance and that very few applications need the second nut adjusted. Square D specifies a ⅜-inch nut driver or socket.

How many turns

Range-nut turns between standard settings (Square D 9013F/9013G)
From	To	Turn the range nut clockwise
20/40	30/50	3½ turns
30/50	40/60	3½ turns
20/40	40/60	8 to 8½ turns

Source: Square D's maintenance bulletin, which presents the table as a guideline.^[1] Pentair's sheet gives about 2½ psi per full turn for its switches.^[2] Switches differ, so treat any figure as a starting point and confirm on the gauge.

The sequence

This follows Square D's procedure.^[1]

Turn off power to the pump at the breaker and confirm it is off.
Reset the tank precharge for the new setting. Drain the water from the pressure tank, read the tank's air pressure with a gauge, and add or remove air until it is 2 psi below the new cut-in (for 40/60, that's 38 psi). Follow the tank maker's instructions where they exist. Read the warning below first.
Remove the switch cover and look before you touch: no leaks at the diaphragm, no corrosion, no burnt wiring, no insects or nests.
Turn the range nut the number of turns for your change. Leave the differential nut alone unless you have a specific reason.
Replace the cover, restore power and let the pump fill the tank.
Test. Open a faucet until the pump starts, close it, and note where the pump shuts off. Repeat the adjustment in small steps if needed.

About raising the precharge

Raising the switch setting means raising the tank's air pressure. Amtrol's manual carries a specific danger warning for exactly this situation — a tank already in service that needs a higher precharge — and warns that adding pressure to a tank that is corroded, damaged or has lost integrity can make it burst.^[3] Inspect the tank first. If it's old, rusty or has ever lost its air charge, don't pump it up: have it evaluated.

What not to do

Don't adjust with the power on.
Don't sand, file or spray the contacts while you're in there. Square D: "Do not sand or file the contacts," and don't use chemicals to clean them.^[1]
Don't test the pump's maximum pressure by running it against a closed valve; Pentair warns of explosion risk.^[2]
Don't narrow the differential to make the pressure feel steadier. Less differential means less water per cycle and more pump starts.
Don't force a switch past its range. Square D's fix when a switch can't be adjusted to the desired pressure is to replace it with one that has the correct range.^[1]

If the adjustment didn't work

After adjusting: problems and likely reasons
Problem	Likely reason
Pump now runs and won't shut off	The new cut-out is above what the pump can reach. Power off and turn the range nut back. See pump can't reach cut-out.
Pump starts much more often	Precharge not reset, or the tank is now too small for the higher setting. See tank sizing.
Pressure dips to nothing just before the pump starts	Precharge is above cut-in. Use the precharge calculator.
Setting won't hold, or switch acts erratically	Worn switch or clogged sensing port. See switch troubleshooting.

Compare 30/50 vs. 40/60 Check my pressure tank