How to Adjust a Well Pump Pressure Switch
A pressure switch well pump adjustment comes down to two nuts under the switch cover: the big one moves the whole pressure range up or down, the small one widens or narrows the gap between pump-on and pump-off. With the power off, a nut driver and a pressure gauge, it's a half-hour job for most homeowners.
The two numbers that matter
Every switch has a cut-in pressure, where the pump turns on as pressure falls, and a cut-out pressure, where it turns off as pressure rises. The difference between them is the differential. A 40/60 switch, for example, has a 20 psi differential.
Common settings include 20/40, 30/50 and 40/60. If your shower goes weak right before the pump kicks on, raising the range a little is usually what people are after.
Before you touch the switch: check the tank
On a bladder or diaphragm tank, the air charge has to match the switch, or the pump will short cycle no matter how carefully you set the nuts.
Boshart's guidance is to set the tank's air pre-charge below the cut-in pressure:
| Switch setting | Pre-charge guidance |
|---|---|
| 20/40 switch | 2 psi below cut-in is the absolute minimum |
| 40/60 switch | 5 to 6 psi below cut-in |
| Any switch | 10% to 20% below cut-in is a suitable range, and about 15% leaves room for gauge error and temperature swings |
To check it, shut the main valve to the house and drain the tank until the gauge on the plumbing reads zero, with the pump off, then read the air valve on top of the tank with a tire gauge. Add or let out air there. If you're raising the switch setting, reset the pre-charge below the new cut-in.
Tools
- A 3/8 inch nut driver or socket
- A tire pressure gauge for the tank's air valve
- A small air compressor or bike pump
- A working pressure gauge on the plumbing near the tank (replace it if the needle sticks)
Step by step
Kill the power
Switch off the pump breaker and confirm the pump won't start.
Take off the switch cover
Look for leaks, corrosion, standing water, lime deposits, pinched or frayed wires, and insect nests before you go further.
Set the tank pre-charge
for the new cut-in, as described above.
To move both numbers together, turn the tall range nut
Clockwise raises the cut-in, counterclockwise lowers it, and the cut-out moves by the same amount, so the differential stays the same. Raise the cut-in by 10 psi and the cut-out goes up by 10 psi too.
To change only the shut-off point, turn the small differential nut
Clockwise raises the cut-out, counterclockwise lowers it, and the cut-in doesn't move.
Make small moves
How far each turn moves the pressure varies, so go a turn or two, then test. Guessing ten turns at once is how people end up with a pump that never shuts off.
Put the cover back on and restore power
Let the pump fill the tank.
Test it
Open a faucet and let water run until the pump starts. Note that pressure, which is your cut-in. Close the faucet and watch the gauge climb until the pump stops: that's your cut-out. Repeat the adjustment if you're not where you want to be.
Mistakes to avoid
- Raising the cut-out past what the pump can make. If the pump can't reach the new shut-off pressure, it runs and runs. Back the setting down until the pump shuts off on its own.
- Ignoring the tank. A switch set higher with the old pre-charge is a recipe for rapid cycling. Fix the air charge every time you change the cut-in.
- Cleaning the contacts. Pitted contacts are normal wear. Boshart says not to sand, file or chemically clean them. If they're burned, replace the switch.
- Working with the cover off and the power on. Never.
When it's a job for a pro
Call a well contractor if the pump won't build pressure even at the old setting, the switch contacts are burned or chattering, there's water in the switch box, or the pressure falls with every tap closed (that's a leak, often in the line from the well or a check valve). A pro can also tell you whether your pump and tank are sized for the pressure you want.
FAQ
Can a well pump pressure switch be adjusted?
Yes. Standard switches have a range nut that shifts the cut-in and cut-out together and a differential nut that moves only the cut-out. Make small changes with the power off and test after each one.
Can I adjust a 30/50 pressure switch to 40-60?
Often, yes. Turning the range nut clockwise raises both settings by the same amount, so a 30/50 can be moved up 10 psi to roughly 40/60. Raise the tank pre-charge to match, and make sure your pump actually shuts off at the new cut-out.
What should your well pressure switch be set at?
Common settings include 30/50 and 40/60, and either works in a typical house. Whatever you pick, set the tank's air charge 10% to 20% below the cut-in.
Why won't my well pump build over 30 psi?
A pump that stalls at a low pressure usually has a problem, not a setting issue: a worn pump, a low water level in the well, a leak in the drop pipe, or a clogged screen or filter. Lowering the switch setting only hides it. Have the well checked before raising anything.
Sources
- Boshart IndustriesHow do I adjust a pressure switch? (opens in a new tab)
- Boshart IndustriesAdjusting the pre-charge pressure of a captive air bladder or diaphragm type tank (opens in a new tab)