Water Pump Short Cycling: 6 Causes and How to Fix Them

Written by Fajar Webarq. Updated October 26, 2026.

Summary

• A pump that switches on and off repeatedly within seconds (short cycling) can come from the pressure tank, a small leak, a leaking valve, the pressure switch setting, or a faucet that is only half open.
• Tank air pressure is measured with the power off and the water pressure released, then set slightly below the pressure switch cut-in point, usually by 2 psi (about 0.14 bar).
• Do not add air to a tank that is rusty or keeps losing air. Tank manufacturer Amtrol warns that such a tank can burst.

A water pump that keeps turning on and off means the pressure in the pipes is rising and falling too fast, so the pressure switch repeatedly connects and cuts power to the motor. The source can be the pressure tank, a small leak, a valve, the switch setting or the way a faucet is used. This guide covers those six causes, how to check tank air pressure according to the manufacturer's manual, and when to call a technician.

Why Does the Water Pump Keep Turning On and Off?

A pump keeps cycling because the reserve of pressurized water in the system is too small or keeps shrinking. The pressure tank stores water pushed by a cushion of air. If that cushion is lost, there is a leak, or a faucet is opened just a little, the pressure quickly drops to the cut-in point and then quickly climbs to the cut-out point, and the cycle repeats.

Boshart, a maker of tank air controls, explains that the air in the tank acts as a cushion that pushes water out between pump cycles. The Shimizu PT-190 BIT manual states that a pump that delivers water straight to the faucet in principle needs a pressure tank, and that a common household problem is a pressure switch that turns on and off with a constant "click-clack."

This symptom differs from a pump that runs without stopping (see water pump won't shut off) and from a pump that only starts again after a few minutes (see the FAQ).

6 Causes of a Water Pump Turning On and Off Repeatedly

The six causes below are compiled from the troubleshooting tables in the Shimizu, Grundfos, K2 Pumps and Everbilt manuals, plus findings from a University of Mataram journal. The first two causes are in the pressure tank, and the rest are in the pipes, valves, switch and faucet habits. The last column shows what you can safely check yourself.

Causes 1 to 5 are listed in the Grundfos JP PS manual (10/2025), the K2 Pumps FAQ and the Everbilt EB-0185 guide (09/2024). Cause 6 is explained in a University of Mataram community service journal (2025).

The tank loses air or its diaphragm bursts

In a diaphragm tank, a diaphragm separates the water from the air. If the diaphragm leaks, water enters the air chamber; the Shimizu PT-190 BIT lists water coming out of the air valve as a sign of a leaking diaphragm. In a tank without a diaphragm, Boshart explains that the air is gradually absorbed into the water until the tank is waterlogged. Some pumps use an air charger to add air, and the Shimizu PS-255 BIT manual lists it as a component.

Air pressure that is too high is also a problem: the Shimizu PT-190 BIT lists it as a cause of the pump switching off and on. That tank leaves the factory with an initial pressure of 3 bar, while the manual asks for the pressure to be set slightly below the ON point of the pump's pressure switch.

Small leaks, valves and a half-open faucet

The manual for the Shimizu SC-015 E controller distinguishes two patterns: a leak below 0.6 liters per minute makes the pump cycle on and off often, while a leak above that figure makes it run continuously. K2 Pumps adds that a leaking foot valve or check valve lowers the pressure so the pump starts again. The University of Mataram journal notes that the clicking sound also appears when a faucet is open a quarter to a half, because the pressure rises and falls and the pressure switch contacts keep opening and closing.

Diagnostic Steps, Starting With the Easiest

Start with observations that need no tools: when the rapid cycling happens and whether the pump starts while all faucets are closed. Only then check the air valve and the tank's air pressure. Checking the valves and the pressure switch comes last because it means opening up or adjusting electrical parts.

1. Watch the pattern. If the clicking only appears when a faucet is open slightly, open the faucet fully or close it tightly. If the symptom goes away, the cause is a half-open faucet.
2. Run the all-faucets-closed test. If the pump starts briefly over and over with no water in use, there is a leak. Check the toilet tank, the garden faucet, the float valve of the water storage tank and the pipe joints, as described in water pump won't shut off.
3. Check the tank's air valve. Switch off the pump's power, remove the valve cap and press the valve core briefly. If water comes out instead of air, Shimizu says the cause is a leaking diaphragm.
4. Measure the tank air pressure using the steps in the next section, then reset it if it is far from the target.
5. Check the valves. If the prime also disappears often, read water pump that must be primed repeatedly. The Shimizu PS-255 BIT suggests cleaning dirt off a check valve that does not close tightly.
6. Leave the pressure switch to a technician if steps 1 to 5 find nothing, because adjusting the switch means opening a cover that holds electrical connections.

How to Check a Water Pump Tank's Air Pressure

Tank air pressure is measured while the pump is off and there is no water pressure in the system, using a tire pressure gauge on the tank's air valve. The target is slightly below the pressure switch cut-in (ON) point. Shimizu does not state the gap, while Grundfos, K2 Pumps, Everbilt and Amtrol use a gap of 2 psi.

1. Switch off the pump's power by unplugging it or flipping its circuit breaker (MCB).
2. Open the nearest faucet until water stops flowing. The reading is accurate only once the water has been drained (K2 Pumps, Amtrol).
3. Remove the cap from the tank's air valve and measure with a tire pressure gauge.
4. Compare the reading with the ON point in the manual or on the pump's nameplate. Add or release air until it sits slightly below the ON point.
5. Put the valve cap back on, switch the pump on and watch whether the cycling returns to normal.

The table below converts the 2 psi guideline to bar and kgf/cm². The editors calculated the conversions with 1 psi = 0.0689 bar = 0.0703 kgf/cm².

Safety limit. The Amtrol Well-X-Trol manual (06/2019) forbids adding air to a tank that has lost air before, is rusty on the outside, or whose pump cycles have become shorter, because these can signal corrosion inside and the tank could burst. Amtrol asks that adjustments be done by a professional, while the Shimizu PT-190 BIT marks it as a repair the user may do. The safe approach: measuring it yourself is fine, but a rusty tank or one that keeps losing air should not be recharged, and you should never exceed the maximum pressure on the tank's nameplate.

Risks of Letting the Pump Keep Cycling

A pump that keeps cycling wastes electricity, makes the motor run hotter and speeds up wear on parts such as the motor and seals. The University of Mataram community service journal (2025) records all three effects. InspectAPedia, a technical reference for home inspection, adds that short cycling can damage the pump controls and even the pump itself.

As a benchmark, the Grundfos JP PS manual limits starts and stops to a maximum of 20 per hour for that pump. Other brands' limits may differ, but a cycle of just two per minute already equals 120 per hour.

When to Call a Technician

Call a technician if the problem lies in the tank diaphragm, the pressure switch or a valve that has to be taken apart, and if the tank shows signs of rust. These parts involve electricity and a pressurized vessel, so a small mistake during repair can lead to pump damage or injury.

• Water comes out of the tank's air valve. The Shimizu PT-190 BIT recommends replacing the diaphragm (accumulator).
• The tank is rusty or keeps losing air after being adjusted.
• The pressure switch setting or contacts need to be checked or replaced.
• A foot valve or check valve leaks and is hard to reach.
• The pump smells burnt or its thermal protector keeps cutting off the motor.

How to Prevent a Pump From Turning On and Off Repeatedly

Prevention means keeping the pressure reserve adequate and avoiding even the smallest leaks. Most steps need no special tools, and the most important one is making sure a pressure tank is installed, with air pressure that matches your pump's cut-in point.

• Make sure there is a pressure tank. Shimizu recommends a tank of at least 19 liters for a jet pump or semi-jet pump serving around 3 to 4 faucets that are usually on at the same time.
• Measure the tank air pressure when the clicking starts to become more frequent.
• Open faucets fully or close them tightly. For low-flow use, the University of Mataram team added a flow switch; discuss this option with a technician.

Frequently Asked Questions

Why does a water pump keep turning off and on?

Pressure in the system quickly falls to the cut-in point and then quickly rises again. The cause may be low tank air, a burst tank diaphragm, a small leak, a leaking valve, a wrong pressure switch setting or a half-open faucet.

What causes a Sanyo pump to turn on and off sometimes?

The causes in this article come from several manufacturers' manuals and apply to pump systems with a pressure switch and a tank, not to one brand in particular. We have not found an official Sanyo manual, so match the cut-in point and tank type to your model's instruction book.

What should the air pressure in a water pump tank be?

Slightly below the cut-in (ON) point of your pump's pressure switch. Grundfos, K2 Pumps, Everbilt and Amtrol use a gap of 2 psi, about 0.14 bar or 0.14 kgf/cm², measured with the power off and the water pressure released.

Why does a water pump run briefly and then stop?

If the pump switches on and off within seconds while water is in use, the cause is in the list above. If the pump stops and only starts again after a few minutes, the thermal protector has probably cut off a motor that got too hot. The Shimizu PS-255 BIT says to wait 20 to 30 minutes, and Grundfos suggests checking for a clogged impeller and the room temperature if this keeps happening.

Next Steps

If the pump now stops normally but loses its prime often, continue to water pump that must be primed repeatedly. If the pump runs without stopping instead, read water pump won't shut off. All the pump maintenance guides are in the Home Water Pump Maintenance Guide.