How to Test a Water Well Pressure Switch

A switch connected to your well's pressure pump monitors the system pressure and instructs the pump to come on when the pressure falls below this value. It also turns the pump off when the holding tank is sufficiently pressurized. If this switch fails, the pump may not come on, it may not turn off or it may run erratically.

You can diagnose a possible switch failure with a simple tests, but you should call a professional if you suspect a problem. Most switches run on 240-volt power, and removing the cap to conduct a more thorough test could get you electrocuted.

It Might Not Be the Switch

Erratic pump behavior is a symptom of switch failure; the pump may not start when it's supposed to, it may not stop or it may start before the pressure falls to the point at which the pump is supposed to start. Several other factors can be responsible for these conditions, though, including:

  • pump or tank failure
  • debris in the pipes
  • loose electrical connections
  • or a tripped breaker.

It may take a plumber to accurately diagnose your system, but there are a few tests you can conduct yourself that can isolate the problem to the pressure switch.

Testing the Pressure Switch

One of the tests you can conduct involves monitoring the pump's cut-in and cut-out pressure, so it helps to know to what these terms refer:

Cut-In and Cut-Out Pressures

The pressure at which the switch instructs the pump to start is called the cut-in pressure, and that at which it instructs the pump to stop is the cut-out pressure. The recommended range between these pressures is 20 psi; most pumps cut in at 40 psi and cut out at 60 psi. These values aren't universal, and yours might be different -- the best way to know for sure is to watch the gauge on the pump and note the pressures at which the pump starts and stops when everything is working as it should.

Testing Strategy

Step 1

Check the breaker that controls the pump; it may have tripped, preventing the pump from switching on. This is a common cause of loss of water pressure in well systems. Reset the breaker.

Step 2

Open a water faucet and let water run while you watch the pressure gauge on the pump. If the pump doesn't start when the pressure falls to its cut-in value, tap the gauge with your finger. The needle may be stuck. If the gauge is faulty, turn off the breaker, run water until there is no pressure, then replace the gauge. Try the test again.

Step 3

Tap the switch housing with a screwdriver if the pump doesn't come on at its cut-in value or it doesn't go off at its cut-out value. The switch is mounted next to the pump, and the housing is usually a rectangular plastic box. If the pump responds to your tapping, the internal wiring of the switch could be loose or there could be dirt or insects inside the housing and clogging the terminals.

Step 4

Put on a rubber glove for safety and wiggle the switch wire. If the pump responds, it's a convincing indication of loose wiring.