Why Does My Pump Keep Starting and Stopping? (Short Cycling Fixes)

Nothing is more annoying—or concerning—than the sound of a pump constantly clicking on and off. You might hear it in your basement, your mechanical room, or out at the wellhead. The motor revs up for a few seconds, shuts down, and then kicks back on moments later.

This behavior is called pump short cycling, and it is a symptom of a deeper issue within your water system. While it might seem like a minor nuisance, ignoring it can lead to expensive equipment failure.

In this guide, we will break down exactly why short cycling happens, the damage it causes, and the practical steps you can take to diagnose and fix pump short cycling before it destroys your motor.

What Is Short Cycling in Pumps?

Short cycling occurs when a pump starts and stops too frequently. Instead of running for a sustained period to fill a tank or meet system demand, the pump satisfies the pressure requirement almost instantly and shuts off, only for the pressure to drop immediately, triggering another start.

For most standard centrifugal or submersible pumps, a [cycle] includes the startup, the run time, and the rest period. If your pump turns on and off rapidly—sometimes every few seconds or minutes—it is short cycling.

Typical warning signs include:

• The pump runs for less than one minute before shutting off.

• You hear rapid clicking from the pressure switch.

• The motor feels excessively hot to the touch.

• Water pressure at the tap fluctuates noticeably (pulsing).

Why Short Cycling Is a Serious Problem

You should never ignore a pump that keeps starting and stopping. Short cycling is arguably the fastest way to destroy an electric motor.

Increased Electrical and Mechanical Stress

Every time an AC motor starts, it draws a massive surge of electricity called 【inrush current.】 This surge can be 5 to 8 times the normal running current. Frequent starts generate immense heat in the motor windings, far more than the cooling system can handle.

Accelerated Wear

It isn't just the motor at risk. The constant torque of starting and stopping hammers your pump's internal components. Seals, bearings, and couplings wear out prematurely. Additionally, your starter contactors (the electrical switches) will pit and burn out much faster than normal.

Reduced Reliability and Efficiency

A short-cycling system is inefficient. You are paying for high-current spikes rather than steady, efficient operation. Eventually, the thermal overload will trip, or the motor will burn out completely, leaving you without water.

Pressure-Controlled Systems: The Most Common Cause

In most residential and light commercial applications, the pressure switch is the brain of the operation. If the brain is confused, the body (the pump) acts erratically.

Narrow Pressure Differential

The most frequent culprit is a narrow pressure band. Your pressure switch has two settings:

1. Cut-in: The low pressure where the pump starts.

2. Cut-out: The high pressure where the pump stops.

If these two numbers are too close together, the pump will hit the cut-out pressure almost immediately after starting. For example, if your pump starts at 45 PSI and stops at 48 PSI, it takes very little water volume to bridge that 3 PSI gap. The pump satisfies the demand in seconds and shuts off, only to restart moments later.

Improper Pressure Sensor Location

Where you place your sensor matters. If a pressure sensor or switch is located too close to the pump discharge without a dampener, it may react to the initial surge of pressure (turbulence) when the pump turns on.

This creates a false reading. The sensor 【thinks】 the system is full and shuts the pump off. Once the turbulence settles, the sensor realizes pressure is actually low and turns the pump back on. This loop can happen multiple times a minute.

System Demand Mismatch

Sometimes the equipment works perfectly, but it is the wrong equipment for the job.

If you have a powerful pump capable of moving 50 gallons per minute (GPM), but your household or facility is only using 2 GPM, you have a demand mismatch. The pump floods the system with water faster than you can use it. The pressure rises instantly, shutting the pump off. As you continue to use that trickle of water, pressure drops, and the oversized pump roars back to life.

This is common in homes where a previous owner installed a 【bigger is better】 pump without upgrading the storage capacity.

Insufficient or Failed Pressure Tank

If you ask a technician, 【Why does my pump keep starting and stopping?】, the first thing they will likely check is your pressure tank.

Pressure tanks (or hydropneumatic tanks) use a cushion of compressed air to store water energy. When the pump runs, it compresses this air. When you open a faucet, the air pushes the water out. This buffer allows the pump to rest while you use small amounts of water.

Two common failures lead to short cycling:

1. Waterlogging: If the rubber bladder inside the tank bursts, the air dissolves into the water. The tank becomes completely full of water. Since water cannot be compressed, there is no 【cushion.】 The pressure spikes instantly when the pump starts and drops to zero instantly when you open a tap.

2. Undersized Tank: If the tank is too small for the pump's flow rate, it fills up too fast. A high-flow pump needs a large tank to ensure it runs for at least one or two minutes per cycle.

Control Valve and Check Valve Issues

Valves control the direction and flow of water. When they fail, chaos ensues.

Leaking Check Valves

A check valve ensures water only flows one way: out of the pump and into your home. If this valve gets stuck open or leaks, water from your pressure tank flows backward into the well or suction line as soon as the pump turns off.

This causes the system pressure to drop immediately. The pressure switch senses the drop and turns the pump on. The pump fills the system, shuts off, and the water leaks backward again. This creates an endless loop of on-off cycling, often occurring even when no one is using water.

Variable Frequency Drive (VFD) Causes

Modern systems often use Variable Frequency Drives (VFDs) to maintain constant pressure by speeding the motor up or down. While usually efficient, VFDs can short cycle if programmed incorrectly.

If the PID (Proportional-Integral-Derivative) settings are too aggressive, the drive will ramp up speed too fast, overshoot the target pressure, and shut down. It then realizes pressure is dropping and ramps up hard again. This is called 【hunting,】 and it creates a surging effect similar to short cycling.

How to Diagnose Short Cycling Step by Step

Ready to fix pump short cycling? Follow this diagnostic logic.

1. Observe the Cycle: Stand by the pump while water is running. Time how long the pump runs. Is it 10 seconds? 30 seconds? A healthy pump should generally run for at least 60 to 120 seconds per cycle.

2. Check the Air Valve: Go to your pressure tank. Locate the Schrader valve (it looks like a tire valve stem) near the top. Briefly press the center pin.

   If air comes out: The bladder might be okay (but check pressure).

   If water squirts out: Your tank is waterlogged (bladder failed). You need a new tank.

3. Watch the Pressure Gauge: Turn off all water taps. Watch the gauge. If the pressure drops steadily while the pump is off, you have a leak—likely a failed check valve or a leak in your drop pipe.

4. Listen to the Switch: If the tank is fine and there are no leaks, watch the pressure switch. Does it click off immediately after clicking on? Your differential settings may be too tight, or the switch nipple might be clogged with sediment.

How to Fix Pump Short Cycling

Once you identify the cause, the solution is usually straightforward.

• Adjust Pressure Switch: Widen the gap between cut-in and cut-out. A standard differential is 20 PSI (e.g., 40/60 PSI). Consult your manual before turning the adjustment nuts.

• Repressurize or Replace the Tank: If the tank is waterlogged, replace it. If the air charge is just low, turn off the pump, drain all water pressure from the system, and use a bicycle pump or compressor to recharge the air to 2 PSI below your cut-in pressure.

• Install a Cycle Stop Valve (CSV): For oversized pumps, a CSV can be a game-changer. It mechanically restricts flow to match your usage, keeping the pump running constantly rather than cycling on and off.

• Clean the Switch Sensor: Sometimes, sediment clogs the tiny tube leading to the pressure switch. Turning off the power and cleaning this tube can restore accurate readings.

Common Misconceptions About Short Cycling

Short cycling is normal for small systems.
False. Even small systems need a minimum run time to cool the motor. If a system is small, it needs a properly sized pressure tank to prevent cycling.

Higher pressure settings solve the issue.
Not necessarily. Cranking up the pressure usually just puts more strain on the pump without solving the underlying control logic or storage issue.

Bigger pumps reduce cycling.
Actually, the opposite is true. An oversized pump fills the system too fast, leading to more frequent stops.

Conclusion

Short cycling is rarely a mystery; it is a mismatch between the pump's capacity and the system's control logic. Whether it is a waterlogged tank, a leaky check valve, or bad switch settings, the result is the same: unnecessary wear and tear on your equipment.

Diagnosing the issue early saves money. A pressure switch costs $30, and a pressure tank costs a few hundred dollars. Replacing a burned-out submersible well pump, however, can cost thousands. Take the time to listen to your system—if it’s clicking, it's calling for help.

Frequently Asked Questions

Can short cycling damage the motor quickly?
Yes. The heat generated from starting can degrade winding insulation in a matter of weeks or months, drastically shortening the lifespan of the motor.

Is a VFD always the best solution?
A VFD is an excellent solution for variable demand, but it is expensive and complex. For simple residential setups, a properly sized pressure tank or Cycle Stop Valve is often more cost-effective.

How many starts per hour are acceptable for pumps?
Manufacturers vary, but a general rule of thumb for submersible motors is to limit starts to fewer than 10 to 15 per hour. Some heavy-duty industrial motors are rated for even fewer.