Equipment pad leaks and where they actually come from

Where do pads actually leak?

The pump lid o ring is first by a wide margin, and it usually presents as a wet ring under the pot rather than a stream. Right behind it are the two drain plugs at the base of the pump, which get loosened before a freeze and never fully retightened, and their small o rings which get lost or reused past their life.

Unions come next. A union is designed to be taken apart, which means it has an o ring and a threaded collar, and both age. A union that has been apart three times for three different repairs is a union whose sealing face has been scratched.

Then the filter. On a cartridge filter it is the band clamp and the large o ring between the two halves, which is the single most common filter leak. On a DE or sand filter with a multiport valve it is the valve spider gasket or the bulkhead connection. On any filter it can be the drain plug or the air relief assembly.

Then the heater connections, then any threaded fitting on the pad. Threaded PVC is the least forgiving joint in pool plumbing, because it seals on tapered threads and it cracks if it was overtightened during installation, sometimes years before it starts weeping.

Is it leaking under pressure or under suction?

Draw the line at the pump impeller. Everything from the pool to the impeller is under suction while the pump runs. Everything from the impeller through the filter and heater and back to the returns is under pressure.

A pressure side leak drips or sprays while the pump is running and slows or stops when it is off. That is the easy kind. You can see it, and the location of the wet patch is close to the location of the fault.

A suction side leak does the opposite. While the pump runs, that pipe is below atmospheric pressure, so it pulls air in rather than pushing water out. There is no puddle. The symptoms are bubbles at the returns, air collecting in the pump pot, a pump that loses prime, and a system that never quite performs.

The odd case is a suction side leak that only drips when the pump is off, because with the vacuum released the water finds its way out through the same opening. A pad that is dry all afternoon and wet in the morning is often exactly this.

Why does a small pad leak matter more than it looks?

Because of where the water goes. A slow drip onto a concrete pad runs to the lowest point, and the lowest point is very often the base of the pump motor or the electrical enclosure. Motors that fail early on otherwise well kept pads have usually been standing in a puddle for a year.

Because of the air. A suction leak makes the pump run partly on air, which means less water cooling the shaft seal, more heat, cavitation noise and reduced flow through everything downstream including the heater and the salt cell. A small air leak degrades the entire system.

And because it is a progress report. Leaks at unions and threaded fittings on a pad that is moving with the soil are telling you something about the pad, not just about that fitting. One weeping union is a repair. Three in two years is a pad that needs looking at as a whole.

What is a homeowner fix and what is not?

Reasonable to do yourself: hand tighten a union collar that has backed off, snug the pump drain plugs, and replace the pump lid o ring with a correct part and a silicone based lubricant made for pool o rings. Those three cover a real share of pad leaks and they need no tools that can do damage.

Also reasonable: cleaning the pad so you can actually see where the water is coming from. A pad with standing water and algae on it hides the source. A clean dry pad watched for ten minutes after startup usually shows you the answer.

Not a homeowner job: anything that involves cutting or gluing PVC, anything on the gas side of a heater, anything involving the filter band clamp on a pressurized vessel, and anything electrical. A filter band clamp in particular deserves respect, because a filter is a pressure vessel and a clamp reassembled incorrectly can separate under pressure.

Also not a homeowner job: chasing a suction side leak. Finding air ingress on a buried line takes pressure testing equipment and experience, and the guesswork version of it involves a lot of digging in the wrong places.

Why do pads start leaking after a dry summer?

Because the ground moved. Expansive clay shrinks as it dries, and a pad sitting on shrinking soil settles unevenly while the rigid PVC connected to it does not want to move at all. Something has to give, and what gives is the joints.

The effect is cumulative rather than dramatic. A pad does not crack in one afternoon. It settles a fraction each dry season, the plumbing takes a little more strain, union nuts back off, threaded fittings that were slightly overtightened at installation develop hairline cracks, and one August the pad is wet.

The same mechanism reverses in a wet spring, when the clay swells and pushes the pad back up. That cycling is harder on joints than either extreme would be on its own, which is why joints on older pads here are the usual suspects rather than the pipe itself.