How to Replace a Well Pressure Switch

Before you buy: is it really the switch?

A lot of "bad switches" are a clogged inlet. Boshart says the tube or 1/4-inch nipple that feeds the switch diaphragm can get blocked with sediment, iron or rust, and a switch that starts when you tap it is a classic sign. Replacing the nipple is the fix Boshart recommends, and you'll do that during a switch swap anyway.

Boshart names a linkage worn from years of use as one real switch failure. Burned or welded contacts, a cracked base or a diaphragm leaking water into the box also mean a new switch. Pitted contacts alone are normal wear, and Boshart says not to sand, file or chemically clean them. If you're not sure, our pressure switch problems page helps you narrow it down.

Match the new switch to the old one

Read the label inside the old switch cover and buy a switch that matches on:

• Pressure range. Common ranges include 30-50, 40-60, 50-70 and 60-80 psi. Stay with what you have unless you've decided to change it.
• Motor rating. The switch has to be rated for your pump's horsepower and voltage. Boshart ties its switches' pump ratings to horsepower and voltage.
• Standard or low-pressure cutoff. If the old one has a lever, decide whether you want the lockout again. Our low-pressure cutoff switch page explains the trade-off.
• Connection. Boshart's switches use a 1/4-18 female pipe thread, which is the usual size.

If only the contacts are worn on a Square D Pumptrol, the maker sells contact replacement kits that include a new diaphragm: 9998PC241 for FSG and FSW switches, 9998PC242 for FYG and FYW. Most homeowners just buy the whole switch.

Tools and parts

• New pressure switch
• New 1/4-inch brass nipple or tube, plus any tee fitting that's corroded
• Thread sealant tape or pipe dope rated for potable water
• Screwdrivers and a 3/8-inch nut driver for the adjustment nuts
• Two adjustable wrenches
• Non-contact voltage tester or multimeter
• Tire pressure gauge for the tank's air valve
• Phone camera for the wiring photo

Step by step

A new low-pressure cutoff switch won't start on its own the first time. Its contacts ship open, so hold the lever at Start until the pump builds pressure.

Mistakes to avoid

• Reusing a crusty nipple. It's the cheapest part of the job and often the actual cause.
• Swapping the line and load wires. The switch still works, but the terminals marked as load stay live with the contacts open. Wire it to the markings.
• Buying a switch rated below your pump. Undersized contacts burn up fast.
• Skipping the tank check. A wrong air charge will short cycle the pump and kill the new switch too.
• Leaving conduit openings unsealed. Boshart warns that bugs and debris getting into the switch create a fire hazard.

When it's a pro job

Hire a licensed electrician or well contractor if you're not comfortable proving a pump circuit dead, if the wiring is aluminum or scorched, or if the pump still won't build pressure with a new switch. HomeGuide puts a pressure switch replacement at $150 to $200 installed, which is cheap insurance against a wiring mistake.