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WATER TANK TYPES: WATER, OIL, EXPANSION, ALL
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  CONTROLS & SWITCHES on WATER TANKS
  INTERMITTENT CYCLING WATER PUMPS
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WATER TANK AIR, HOW TO ADD
  WATER TANK AIR VOLUME CONTROLS
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  WATER TANK AIR IN BY DRAINING
  AIR HOW MUCH TO ADD
  AIR HOW OFTEN TO ADD
WATER TANK REPLACEMENT
WATER TANK PRESSURE CALCULATIONS
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What Causes "Water Pump Short Cycling" - a water pump turning on and off too rapidly
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How to diagnose & correct short cycling "on-off" of the building water pump

How to adjust the water pump pressure control switch

How to add air back to a water pressure tank

Well pump & water tank diagnosis & repair procedures

This article describes how to diagnose the loss of and need for air in a water tank, how to add air to a building water pressure tank, and how to detect and correct air and water leaks in a building water supply system where a private well is the water source. We also discuss how to adjust the building water pressure by setting the cut-in and cut-out pressure on the pump pressure control switch. Several alternative procedures for adding air to a water pressure tank are described below along with advice about what to do when things go wrong, such as finding air and water leaks. Readers of this document should also see Water pump and pressure tank repair diagnosis & cost an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost. © 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

CAUSES OF SHORT CYCLING - What causes short cycling of a water pump?

The most-common cause of pump short-cycling is loss of air in the water pressure tank. This is the topic discussed at length below, and corrective steps are detailed. However there could be other, less common plumbing problems that cause this symptom. Before "fixing" a problem it's useful to identify the correct problem, less we waste time, effort, and money. Some water pump short cycle causes include the following:

Loss of sufficient air charge in the water tank - this is a common problem with older water tanks, and its remedy is discussed in great detail below at SIGNS OF AIR LOSS. This website tells you how to restore lost air in the water tank, starting at HOW TO ADD AIR.

Photograph of a water pump pressure control switch

A defective water pressure control switch. Switch contacts can burn-up, or the opening into the switch which senses the water pressure in the system can become clogged with sediment or debris. This usually shows up as failure of the pump switch to turn on or off at all, rather than short cycling. But the switch could be damaged or improperly adjusted, causing "short water pump cycling."

Technical note: Clogging of the Water Pump Pressure Control Switch if your water has a high level of silt, debris, or minerals, it's possible that the orifice through which the pressure switch senses the water pressure in the system has become clogged.

A clogged water pump pressure control switch will often fail to turn on at all, even though the pressure in the system has dropped below the water pump "cut in" pressure. On rare occasions we can tap on the switch and it will begin working again, but not for long, and not reliably. Another water pressure control switch failure is the rupture of a rubber disk or "bladder" inside the switch itself. If you detect or suspect a defective pressure control switch, try replacing it with a new one.

A blockage in the water supply piping. For example, a clogged or nearly-clogged water filter can cause the pump control to cycle on and off rapidly. This is because the blockage causes water pressure (between the pump and the filter) to rise very rapidly when the pump turns on. The author once replaced a pump control switch only to discover that the real problem was a clogged filter, so check this item if you have filter(s) installed on the system.

A clogged water filter can block water flow between a pump and water tank or between a water tank and the rest of the building. Try changing the water filter by installing a new cartridge; temporary diagnosis can be made by simply removing a suspect water filter cartridge from its canister entirely. I've also seen a clogged water filter cause water pump short cycling, with a rapid "on-off" pump cycle (which is bad for the pump and pump relay switch.)
Technical note: the same clay, silt, or other debris that clogs a water filter can clog up the pressure sensing opening in the bottom of a pump pressure control switch, as we discussed just above. So if you are looking for a clogged filter, if changing the water filter does not correct a problem with the water pump cycling operation, also consider a possibly-clogged pump pressure switch.

Too much air in the water pressure tank - overcharging: If a well pump pressure control switch is set to cut on at 30 psi and off at 50 psi, at the cutoff point the water tank is empty (a bladder type captive air tank) or nearly empty (a traditional water tank) of water, and the air pressure in the tank is about at 30 psi. The well pump comes on and re pressurizes the tank with incoming water, until the tank pressure of both air and water increases to the pump cut-off point of 50 psi. If someone puts too much air in a conventional water tank (overcharging) the excess air usually simply blows out of a nearby faucet the next time the water is run, and the system will correct itself. But if someone overcharges a captive air water tank the excess air can't escape.

Overcharging when water tank is full: If the previous air charge was set to 50 psi and the system was working normally, and you've now put in a little more than 50 psi, and if you did this deed when the water tank was full or close to full (the pump has pumped up to its shutoff point) you've increased the volume of the air above the water-bladder and therefore decreased the volume of water that will be in the tank on future run cycles. This reduced water volume in the tank will shorten the pump on-cycle and depending on how much air you put in, it could give a very short pump-on cycle or cause pump "short cycling".
Overcharging when water tank is empty: If you pumped just over 50 psi into the air portion of the tank above the water bladder when the pump was turned off and the water tank was empty it will be like having no water/pressure tank on the system at all. When you open a faucet the pressure in the system immediately drops to close to zero, the pump comes on immediately, and because water is not very compressible, the pump cuts off almost immediately, unless you are running lots of water so fast out of the piping that the pump can't catch up to its cutoff point. In that case the pump will run continuously until you turn off the water, then the pump will shut off right away.
Overcharging can damage a water tank - safety warning: overcharging can damage or even break the bladder in a captive air type water tank, converting it to a (short-lived, poor performing) more traditional bladder-less system. The water bladder might also be damaged if water pump pressure is set too high though both of these don't seem highly likely. But watch out! overcharging a water tank with very high air pressure is very dangerous and could cause a water tank to burst, causing severe injury. Don't rely on the presence of the relief valve.
Effects of ambient air temperature on water tank and pump control operation are not normally any concern whatsoever, but in the off chance that your water tank is installed in an unusually hot or cold location, you'll want to review The mathematics to calculate exactly how much difference a given air pressure or air volume change makes inside a water tank is presented in our companion article Water Tank Pressure Calculations
Adding air when previous charge was too small: If the previous air charge in the water tank above the water-bladder was too small in volume and the pump was short cycling, adding more air to the water tank would increase the draw-down time or water volume taken out of the system before the pump has to come back on. This would reduce rather than increase pump short cycling.
How to correct an improperly-charged water tank: If your water tank has been overcharged and is a bladder type you'll probably have to turn off the pump, let all the water out of the tank, and then reset the air charge to the factory-specified pressure for your pump system - probably a little under 20 psi for a 20-40 water pump system or a little under 30 psi for a 30-50 water pump control system. The procedures for properly charging a water tank with air are discussed in complete detail at HOW TO ADD AIR.

A defective captive-air water tank bladder: it sounded so weird we didn't believe it at first, but one reader explained that the water-containing bladder in their WellXTrol type water tank had collapsed and become stuck on itself. The effect was that the tank would accept only a very small volume of water before the stuck-up bladder would reach the pump shut-off pressure. The bladder was replaced and things got back to normal.

An air leak at a rust-perforated, leaking water tank can lose the air charge in the water tank along with the leaking water. See Older steel Tanks for photos and text describing how this happens and how you might spot an intermittent air leak from a faulty water storage tank.

A water leak somewhere else in the system, causing tank pressure to drop too rapidly regardless of actual water use. An example might be a hidden plumbing leak in the building, or a leak in the water line between the well and building, or a leak in the piping within the well itself. If the system has this defect you'll hear the pump coming on and off periodically even when (as far as you know) no plumbing fixture is running in the building. If the leak is severe, the pump may run continuously or nearly so.

Before digging up well lines one should check for a running toilet - the most common leak which is missed in buildings. In humid climates a running toilet can often be spotted by the constant presence of condensation on the outside of the toilet tank. Since some running toilets can be hard to spot, we use septic dye, or sometimes just food coloring, in the toilet water tank to prove that the tank is leaking into the bowl below.

Well piping foot valve leaks: in some cases a defective foot valve in the well can cause water to drain back out of the building system into the well, dropping pressure in the water tank and causing the pump to run mysteriously. The "foot valve" is an anti-siphon device intended to hold water in the pipe that rises up inside the well after the pump has shut off. If the foot valve is damaged you'll need a plumber to pull the well line and replace the valve. The foot valve itself is an inexpensive part but pulling the well line can be costly. On the author's well the foot valve lasts typically about 20 years.

Ask your plumber, as this expert may know other causes and remedies that I've not thought of.

PLUMBING TOPICS
OIL TANKS
SEPTIC SYSTEMS
WATER PRESSURE REPAIR GUIDE & COSTS
WATER PRESSURE LOSS DIAGNOSIS GUIDE
  WATER PUMP PRESSURE CONTROL ADJUSTMENT
  WATER PUMP PRESSURE CONTROL REPAIR
WATER PUMPS & TANKS & WELLS
WATER PUMP CONTROLS & SWITCHES
PUMP TYPES & LIFE EXPECTANCY
WATER PUMP & TANK SAFETY
WATER SUPPLY & DRAIN PIPING
WATER TANK TYPES: WATER, OIL, EXPANSION, ALL
WATER TANK LIFE EXPECTANCY
WATER TANK REPAIRS
  CONTROLS & SWITCHES on WATER TANKS
  INTERMITTENT CYCLING WATER PUMPS
  SHORT CYCLING WATER PUMPS
  SHORT CYCLING DETECTION
  SHORT CYCLING CAUSES
  WATER TANK AIR LOSS SIGNS
WATER TANK AIR, HOW TO ADD
  WATER TANK AIR VOLUME CONTROLS
  WATER TANK AIR ADD AT AIR VALVE
  WATER TANK AIR IN BY DRAINING
  AIR HOW MUCH TO ADD
  AIR HOW OFTEN TO ADD
WATER TANK REPLACEMENT
WATER TANK PRESSURE CALCULATIONS
WATER TANK SIZE & VOLUME
WATER TANKS HOW THEY WORK
WATER TESTING
WELLS CISTERNS & SPRINGS
WELL LIFE EXPECTANCY
More Information

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Water Tank Maintenance & Repair Chapter Index

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Water pressure tank failures & water pump short cycling diagnosis and repair
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Lead Contamination in Drinking Water: Testing & Correction - Advice (This Article)
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Water testing for Pesticides: comprehensive and pesticides-example parameters
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