Well Pump Short Cycling

Diagnose "Water Pump Short Cycling" & Restore Air in a Building Water Tank

Definition of water pump short cycling rate or frequency

Short cycling of a water pump means that the water pump or "well pump" turns on and off too rapidly or too frequently when water is being run in the building. "Short cycling" means switching on and off every 30 seconds or less.

Watch out: Extreme water pump short cycling may occur every second or less and means you should turn off the pump system to avoid damaging the pump or controls.

The most common cause of a short cycling water or well pump is loss of air pre-charge in the water pressure tank. A bladder type water tank shouldn't have this problem unless the bladder is damaged. For bladderless water tanks, simply turn off the pump, drain off water pressure, and set the tank air pre-charge to 2 psi below the pump CUT-IN pressure.

Here's a typical reader question typical of pump short cycling problems:

9/1/14 William said: my well pressure switch keeps clicking on and off rapidly

How fast is "rapid cycling" or pump short cycling?

Good question.

IT depends on tank size, and more, on the water outflow or usage rate, and also the pump's pumping rate capacity in gpm for the whole system including total vertical lift, piping restrictions & distances.

If a pump, tank, piping, well are in perfect condition and the pump is cycling on and off for a moderate water flow usage rate such as someone running a bathroom sink faucet, then if the pump is turning on and off more often than every 30 seconds I'd want a larger pressure tank.

The pump manufacturers, are, however the final authority on this so you'll want to check with the company who makes your tank.

Certainly if a pump under any circumstances is turning on and off every few seconds or less, something's seriously wrong and the pump or its controls are likely to be damaged or to have a short life.

Watch out: For pressure boosting pumps that do not use any pressure tank (the control that turns the pump on and off is built into the pump), the pump turns on as soon as a plumbing fixture is opened to run water and runs all the time water is being run.

If the pressure booster pump that does not use a pressure tank (such as the new Grundfos Scala2 tankless pressure pump) is cycling on and off repeatedly in short intervals further investigation is needed: there may be a plumbing leak soaking your building.

Watch out: with tankless booster pumps: any small leak such as a running toilet or pinhole leak in a pipe may cause the pressure booster pump to cycle on and off more frequently than the manufacturer intends - risking damage to the pump.

Why a Water Pump "short cycles" on and off rapidly

Details About Short Cycling Water Pumps

The "water storage tank" is doing more than storing water. Its air charge acts like a spring to smooth the delivery of water in the building. If the building water supply pump is "short cycling" - coming on and off rapidly, you may need to add air to the water pressure tank.

This step is important to protect your private pump and well from damage due to short-cycling due to loss of air in the pressure tank. Short cycling of the pump motor can burn up the pump relay control.

The minimum that a building owner or occupant needs to know is that short cycling is an on-off cycle of the water pump in a house with a private water pump and water supply well system. The "short cycling" water pump is turning on and off rapidly, perhaps every 10 to 20 seconds or even more frequently.

Water pump short cycling can damage the pump or controls. Repair is needed at one or more of: the water pressure tank, water pump pressure control switch, water pump, water filter, or the well or building water supply piping. If you are not interested in tackling this easy repair yourself, call a plumber.

The sketch shown at the top of This article shows the components of a typical residential water well, water pump, water pressure tank, and water pump control system. Below we include other drawings and photographs of wells, water tanks, and their associated valves and controls.

At some properties the well pump may be inside rather than in the well as in this drawing, and on your tank the water pressure gauge may be mounted on a special air volume control fitting on the back of the water tank itself rather than as shown in this sketch. Sometimes people think this water tank is to "store" water for use in the building. That's rarely the case. Usually water is "stored" by being present in the well and in the ground around the well.

If a pump-operated water supply system is turning on and off rapidly (every few seconds) it would be smart to turn off the water or turn off electric power to the water pump and call a plumber promptly.

If your water pump comes on at odd times but is not short-cycling,

see INTERMITTENT CYCLING WATER PUMPS.

Can the pressure switch setting causing short cycling of a pump?

My airbladder tank pressure came pre set at 38psi but the pressure switch is 20/40 is this causing the switch to cycle on off on off? second question, there does not seem to be water in the tank,why? i get water from the spigot with pressure and the guage jumps right from 20 to 40 and back again. why? - Patty 9/17/12

Reply: pressure tank [starting pressure at installation] should be 2 psi below the cut in pressure of the pump

Patty,

As long as the differential between CUT-IN pressure and CUT-OUT pressure is 15-20 psi, the pressure switch ought not be the cause of pump short cycling.

Usually it's a water tank air charge pressure problem.

The pressure in the pressure tank should always be 2 psi below the cut in pressure of the pump. First, check the gauge when the pump first kicks in before shutting down the pump. Then, turn off the pump. Shut the water supply off to the pump, drain the pressure tank by opening the faucet furthest from the pressure tank, then release all the air from the pressure tank.

Refill the tank with air to 18 psi if the pump is actually cutting in at 20 psi. When you turn the pump back on it will fill the pressure tank and will stop cycling unless you have a leak somewhere or dirty filters. - reply from WaterWorks 9/21/2012

Watch out:  After adjusting nut#2 you may need to check the actual operating water pressures in your system and adjust nut#1 to be sure that you are not pushing the cut-out (upper pressure) so high that the water pump never turns off (dangerous).

Or in a contrary case if you completely loosen the smaller nut #2 (dfifferntial adjustment) so that the pump differential between cut-in pressure and cut-out pressure is very small the water pump may short cycle on and off rapidly when water is being run in the building.

If short cycling seems to be the problem with your water pump, this separate article

WATER PUMP SHORT CYCLING CAUSES describes the most common causes of this problem.

We also provide a complete

WATER PUMP SHORT CYCLING DIAGNOSIS TABLE that lists all possible causes of well pump rapid cycling on and off.

If you are not sure what "water pump short cycling" means or how it is recognized,

read SHORT CYCLING WATER PUMP.

Intermittent water pump cycling is a different problem which is discussed

at INTERMITTENT WATER PUMP CYCLING means that the water pump comes on for no apparent reaso

...

How do we Detect Short Cycling of a water pump? What do we do?

Normally the "pump on" cycle is 30 seconds to 90 seconds or longer, depending on water tank size, and the "pump off" cycle is the same or longer.

What is Water Pump or Water Tank "Short Cycling" - rapid on and off water pump

Short cycling of the water pump means that the water pump keeps turning on and off rapidly whenever you're running water at one or more fixtures in the building. The pump on-off cycle may be perhaps every few seconds, or perhaps every 10-20 seconds. This is a problem, which we diagnose, discuss, and for which we offer repair procedures below.

The minimum that a building owner or occupant needs to know is that short cycling can damage the pump or controls, and that action is needed.

These short cycling problems happen with both in-building jet pumps and with in-well submersible pumps. It's trickier to notice a short cycling submersible pump since you won't hear the pump motor, but you will hear the pump relay clicking on and off, or you can see the water pressure gauge cycling up and down rapidly.

If you are not interested in tackling this easy repair yourself, call a plumber. If the system is turning on and off rapidly (every few seconds) it would be smart to turn off the water or pump and call a plumber promptly since if you let this problem continue you're likely to damage a pump control or pump motor (expensive).

You can tell if your water pump system is "short cycling if:

• Water pressure pulses,
  
  that is the pressure goes from strong to weak, at a short time interval ranging from just a few seconds to perhaps a minute.


• The water pump turns on and off rapidly
  
  on the same time interval. You may hear the pump motor running and stopping and running again.


• The water pressure gauge oscillates from high to low pressure rapidly
  
  on the same time interval. You can use this method if your well pump is not located in the building where you can hear it. The pump itself may be outside in a well pit or down in the well itself (a submersible well pump).

If you don't know how to find your pump pressure gauge, pressure controls, switches and controls,

see WATER PUMP & TANK CONTROLS & SWITCHES

How to Detect a Short Cycling Water Pump and Tank

We give more description of how to detect short cycling of the water pump

at SIGNS OF AIR LOSS

How to Diagnose the Cause of a Well Pump that Keeps Turning On and Off

Watch out: before "fixing" a short-cycling well pump, you'll want to try for an accurate diagnosis of its cause - the right fix is cheaper than a whole collection of wrong fixes.

See WATER PUMP SHORT CYCLING CAUSES for an explanation of the most common causes of well pump short cycling

See WATER PUMP SHORT CYCLING DIAGNOSIS TABLE for a table that lists the all of the possible causes of well pump short cycling

How to Fix a Short Cycling Water Pump and Tank

Our articles listed above, WATER PUMP SHORT CYCLING CAUSES

and WATER PUMP SHORT CYCLING DIAGNOSIS TABLE list the corrective steps for a short cycling well pump - depending on the cause.

If it turns out that you want to just try the easy, quick, above-ground "fix" of adding air to the water tank, we describe how to correct water pump short cycling, in great detail and giving several methods,

at WATER TANK AIR, HOW TO ADD for conventional water tanks that do not use an internal bladder.

Bladderless water pressure tanks,

because the air charge and water are in the same container, can lose their air charge over time (air is absorbed into the water) and may need air added.

At BLADDERLESS STEEL WATER PRESSURE TANKS we discuss waterlogged water tanks and well pump short cycling.

See WATER TANK AIR, HOW TO ADD for details on how to add air to a water pressure tank.

Bladder type or captive-air water pressure tanks 

and their repairs are described at WATER TANK TYPES

and at WATER TANKS HOW THEY WORK.

At WHAT GOES WRONG WITH an INTERNAL BLADDER TYPE WATER TANK?we discuss the combination of well pump short cycling and a burst water tank bladder and how this condition is identified and repaired.

See this detailed article on bladder-type "captive air" water tank diagnosis and repair:

at WATER TANK BLADDERS & CAPTIVE AIR

Do I Need a New Water Tank?

Question: should I replace my old water tank?

We just had our pump replaced after 18 years. Total cost with tax was $2400. Project was done on emergency basis on a Friday night and we were really stuck. During his visit the plumber/owner suggested we consider a larger pressure tank than our 20 gallon unit, also recently replaced.

The system worked well for many years and I don't see the need to purchase another larger tank. Any thoughts? - Wayne Ouellette

Reply: maybe not.

If your water tank is a newer bladder type, even a smaller 20-gallon tank gives the equivalent of a larger old style (non-bladder) tank in the draw-down cycle - the amount of time that you can run the water before the pump has to come on.

As long as your pump is not WATER PUMP SHORT CYCLING (which may shorten pump life), the gain from a larger tank is probably not much. If your tank is an older type with no internal bladder, the reason to go to a newer tank would be reliability and reduced maintenance.

Some Reasons to Consider a New Water Tank

1. The water tank is perforated, damaged, or leaking - you need a new one
2. The water pump has constant WATER PUMP SHORT CYCLING problems and the water tank is an older non-bladder type you can reduce the frequency of water tank maintenance (adding air) and eliminate problems with automatic air volume controls that try to add air for you by installing a new bladder type water pressure tank.
   
   At WATER TANK TYPES: WATER, OIL, EXPANSION, ALL we explain the different types of water tanks.
3. Your well has a poor flow rate and you often run out of water. Less costly than drilling a new well is the addition of greater water storage capacity in one or a series of larger water tanks.
   
   But first see WATER PRESSURE LOSS DIAGNOSIS & REPAIR,
   
   and see WATER PRESSURE PUMP REPAIR GUIDE.

Watch out: before you go to the trouble and expense of replacing a water pressure tank, make sure that you have correctly diagnosed the problem that you are "curing" - you wouldn't want to replace a water tank only to find that you still have the water pressure or quantity problem because another, perhaps less costly, part was at fault.