A residential swimming pool is meant to be a source of relaxation—not confusion and wasted water. So when your pool’s autofill system runs constantly, it’s a sign that something is wrong. A properly functioning autofill should only run intermittently to replace water lost to evaporation or splashing. But when it seems to be flowing nonstop, homeowners need to dig deeper into the cause. This isn’t just a minor annoyance—it can lead to skyrocketing water bills, chemical imbalances, and even hidden structural damage if a leak is involved.
In this article, we’ll delve into the potential reasons why your pool’s autofill is constantly running. We’ll walk through causes ranging from natural water loss to mechanical failures, plumbing issues, and hidden leaks. Whether you’re troubleshooting the problem yourself or considering whether to seek professional help, this guide will provide you with the knowledge you need to make informed decisions.
How a Pool Autofill System Works
An autofill system maintains your pool’s water level by automatically adding water when the water level drops below a set point. Most systems utilize a float valve similar to the one found in a toilet tank. The float rises and falls with the water level. When the level drops, the float drops, too, opening a valve that allows fresh water to flow into the pool. Once the correct level is restored, the float rises and closes the valve, shutting off the water supply.
This process is simple but effective—until something interferes with it. If your autofill is running nonstop, it typically means one of two things:
- Water is being lost from the pool faster than expected, and the autofill is trying to keep up.
- The autofill valve itself is malfunctioning, allowing water to flow even when it’s not needed.
Let’s examine each of these scenarios and their causes.
Normal Water Loss: Evaporation and Splash-Out
Before assuming the worst, consider the natural water loss your pool may be experiencing. On average, pools lose about 1/8 to 1/4 inch of water per day to evaporation, especially in hot, dry, and windy climates. The rate can increase dramatically if:
Your pool is in full sun with no shade
The air humidity is low
There is constant wind across the surface
The water temperature is elevated
Additionally, splashing from swimmers, automatic cleaners, or water features such as fountains and waterfalls can contribute to rapid water loss.
A pool losing 1/4 inch of water a day can shed hundreds of gallons. Your autofill might run several times a day to keep up with this loss—especially in large pools.
How to test:
Try a bucket test. Place a 5-gallon bucket on the pool’s steps (partially submerged) and fill it to match the pool water level. Turn off the autofill. After 24 hours, compare the water loss inside the bucket to that of the pool. If the pool level has dropped significantly more than the bucket, it is likely due to a leak, not just evaporation.
The Red Flag: Hidden Pool Leaks
If evaporation doesn’t explain the problem, your constantly running autofill may be compensating for a leak. This is a common scenario that often goes undetected for weeks or months.
Structural Leaks
Leaks can occur anywhere in the pool shell, especially around:
Skimmer throats
Pool light niches
Return fittings
Cracks in the plaster, tile, or concrete
Main drains
Over time, ground movement, aging materials, or faulty construction can allow water to seep through small gaps. Since the autofill is replacing the lost water, you may not even notice the water level is dropping.
Plumbing Leaks
Your pool has a network of underground pipes that circulate water between the pump, filter, and heater. These pipes can develop:
Cracks
Loose connections
Damage from tree roots or ground shifting
If a return line leaks under pressure, it will leak water while the pump is running. If a suction line leaks, it can draw in air when the pump is running and allow water to drain out when the pump is off. These underground leaks can be massive but completely invisible on the surface.
Equipment Pad Leaks
Leaks from your equipment—such as filters, pumps, heaters, or chlorinators—are another possibility. A faulty backwash valve, a cracked filter housing, or a leaky union fitting can cause water to spill, which the autofill replaces without your notice.
Signs of leaks include:
Air bubbles in the return jets
Constant water around the pool equipment
Green or extra-lush patches in nearby landscaping
High water bills despite normal usage
A constantly running autofill is one of the most common symptoms of a hidden leak.
Autofill Valve Malfunction or Misadjustment
If the pool is retaining water just fine, the issue may be with the autofill valve itself. Several things can go wrong:
Debris Blocking the Float Valve
Dirt, leaves, sand, or calcium buildup can prevent the float from rising properly or prevent the valve from sealing shut. This creates a constant trickle of water even when the pool is at the correct level.
Solution: Open the autofill box, clear out any debris, and clean around the float mechanism. This is a common and easy fix.
Improper Float Setting
The float may be set too high, causing the pool to overfill and continuously drain out the overflow. The autofill continues to run, maintaining this incorrect water level.
Solution: Adjust the float so it shuts off when the pool is at mid-skimmer level—before the water reaches the overflow drain.
Worn or Broken Valve Parts
If the internal seals of the valve are worn or the float is damaged (sometimes hollow floats fill with water), the valve may not shut off completely.
Solution: Replace the float assembly. Most systems utilize standardized float valves that are relatively inexpensive and easy to replace.
Leaking Autofill Supply Line
Sometimes, the autofill itself is fine, but the water line feeding it is leaking underground. This can cause water to run continuously even if the valve is “closed.” This is a tough one to detect without professional equipment.
Underground Plumbing Leaks and Slab Issues
In some cases, the water added by your autofill never even reaches the pool. It could be leaking out before it enters the pool, especially if:
The autofill’s equalizer line (which connects the fill valve to the pool) is leaking underground
The autofill’s pressurized supply line is cracked and leaking below the deck
The autofill is connected to a return line or skimmer that has a leak
Water might be leaking underground where it won’t be visible at the surface. You might only notice signs like:
Unusually wet soil near the pool or equipment
Pavers lifting or sinking
A spinning water meter when no other water is being used
Leaks like this can waste thousands of gallons per month and drive up utility bills. More importantly, they can cause soil erosion, voids under the pool deck, or foundation damage over time.
High Water Table and Hydrostatic Pressure
In rare cases, a high groundwater level can impact your pool’s autofill. If water is entering your pool from below through the hydrostatic valve, it could cause the water level to rise unexpectedly and trigger the overflow drain.
This can trick homeowners into thinking the autofill is running too much when, in fact, natural water is pushing in from the ground. On the flip side, if the hydrostatic valve is broken, it could be leaking pool water out through the main drain.
If you’re in a low-lying or flood-prone area, especially after periods of heavy rain, this could be part of the problem.
Overflow Drains and Autofill Plumbing Design Issues
Some pools are built in a way that creates a perpetual loop of filling and draining:
The autofill is set too high
The pool overflows into the drain
The autofill continues to run to maintain that high level
Water continuously exits via the overflow drain
This is especially problematic if the autofill and overflow are plumbed close together or if the autofill canister doesn’t equalize water pressure properly.
This results in a silent and continuous water loss that is technically not a “leak” but still wastes water and chemicals.
Why You Shouldn’t Ignore a Constantly Running Autofill
Letting this issue go unchecked can result in:
Water waste – You could lose hundreds or thousands of gallons per week
Increased water bills – A leak can easily add $50–$200/month to your utility cost
Chemical imbalance – Constant dilution throws off chlorine, pH, and alkalinity levels
Structural damage – Long-term leaks can erode soil, destabilize the deck, and crack the shell
Your autofill system is designed to help, but when it runs constantly, it masks serious problems. Don’t wait for a bigger issue to arise.
When to Call a Leak Detection Professional
If you’ve:
Performed a bucket test and confirmed excessive water loss
Cleaned and adjusted the autofill with no improvement
Inspected the equipment pad and found no obvious leaks
Noticed lush grass patches or damp areas near the pool
Seen your water bill rise without explanation
… it’s time to call a professional.
Why Precision Leak Detection?
At Precision Leak Detection, we specialize in finding and diagnosing leaks in residential swimming pools. Using advanced methods like pressure testing, ultrasonic listening, dye testing, and video inspection, we can locate even the most hidden leaks without guesswork.
We don’t just find the leak—we help you understand the issue, recommend permanent solutions, and provide expert guidance to protect your pool, your wallet, and your property.
If your pool’s autofill is constantly running, don’t ignore it. Contact Precision Leak Detection today for a professional evaluation. Whether you’re in Boca Raton, Lake Worth, Palm Springs, Highland Beach, or anywhere else in Palm Beach County, we’re proud to serve homeowners throughout the area with expert leak detection you can trust.
Let us help you solve the mystery behind your pool’s water loss so you can get back to enjoying it—without the stress, waste, or expensive surprises.
