Waterlogged tank

Short definition

A waterlogged pressure tank has lost the air cushion that keeps a well pump from cycling on every fixture use. The classic symptom is a pump that switches on and off rapidly whenever water flows. Confirm by tapping the tank — a dead “thud” means waterlogged. Recharge if the bladder’s intact; replace if it’s ruptured. Common WA well-system failure.

What it is

A well system stores pressurized water in a bladder pressure tank between the well pump and the house plumbing. The bladder is pre-charged with air on one side and fills with water on the other; that air cushion lets the tank deliver several gallons before the pump has to run again. When the bladder ruptures or the air pre-charge leaks out (usually through the Schrader valve at the top), the tank fills with water and stops cushioning anything.

The symptom is unmistakable once you know it: every time you open a faucet, the pump kicks on, runs for ten seconds, and shuts off — over and over. That’s “short-cycling,” and it kills well pumps fast. Pump motors are designed for 15–30 starts a day. A waterlogged tank can push them to 200+.

How to confirm:

1. Tap the tank with a knuckle. A healthy tank sounds like a wooden barrel — hollow “whoosh” up top, dull “thud” near the bottom where water sits. A waterlogged tank sounds dead-thud all the way up.
2. Press the Schrader valve at the top of the tank. Air should hiss out. If water sprays, the bladder is ruptured — replace the tank, no recharging will help.
3. Watch the pressure switch. A waterlogged tank cycles the switch every few seconds during use.

The fix, if the bladder’s intact:

1. Drain the tank fully — open the lowest faucet in the house with the pump breaker off.
2. Recharge the bladder with a bicycle or air pump while system pressure is at zero — to about 2 psi below the pump’s cut-in pressure (so 28 psi for a 30/50 system, 38 psi for a 40/60).
3. Reactivate the pump and refill.

The most common DIY error: charging the tank without draining it first. The gauge reads system water pressure, not bladder pressure, and you can’t get a true reading until the water side is empty.

Why it matters to a homeowner

A waterlogged tank is one of the most common — and most preventable — well-system failures in WA. Bladder tanks last 5–10 years; replacement costs $300–$800 installed. But ignoring the short-cycling can burn out the pump motor, which is buried in the well casing and costs $1,500–$4,000 to replace. The waterlogged tank is the cheap, early-warning version of the expensive pump failure.

If you have a private well — common on the Olympic Peninsula, Mason and Jefferson Counties, parts of Snohomish, Pierce, and Kitsap — knowing the tap-the-tank test puts you ahead of most homeowners. Pre-purchase well inspections include a pre-charge check; insist on one if you’re buying a well home.

Common failure modes

• Bladder rupture — most common; replace tank.
• Schrader valve leak — slow loss of pre-charge over months; replaceable on some models, but full replacement is often easier.
• Pre-charge never set correctly at install — gradually waterlogs from day one.
• Pressure switch failure mimicking waterlogged tank — cycles fast, but tank tap-test reveals tank is fine. Different fix.

Common variants

• Waterlogged tank (well system) vs. air locks in supply. Both involve air-water imbalance, but waterlogging is loss of air pre-charge in a pressure tank; air locks are unwanted air pockets in supply lines.
• Pressure tank vs. expansion tank. A pressure tank is on the well-pump side; an expansion tank is on the water-heater side of a closed-loop hot-water system. Different purposes, both can fail.
• Waterlogged tank vs. broken pump impeller. Both cause poor performance — waterlogging causes short-cycling; a broken impeller causes low pressure with the pump running continuously.

Washington note

Roughly 1 in 8 WA homes uses a private well, concentrated heavily in Mason, Jefferson, Clallam, Kitsap, and rural Snohomish, Pierce, and parts of Skagit counties. The Department of Ecology and county health departments don’t regulate pressure-tank maintenance — it’s entirely on the homeowner. That’s why waterlogged-tank failures often only get noticed after the pump motor burns out months later.

If you’re buying a WA well home, the tank’s age is critical due-diligence. A 12-year-old bladder tank is almost certainly nearing failure, regardless of whether it’s currently waterlogged. Budget for replacement.

For homes on community wells (small water systems regulated by DOH under WAC 246-290), the system operator handles tanks at the source — but the home-side pressure tank, if any, is still yours.