How-to
Replacing a Well Pressure Tank: When, Which Tank and What the Job Involves
A tank swap is one of the more routine jobs on a well system. The parts that decide whether it goes well are settled before the old tank is unhooked.
On this page
Replace the tank when water comes out of its air valve, when it is rusting or weeping, or when its air charge keeps disappearing. Choose the new tank by the pump's flow, not the size of the old one. The job itself is short: power off, drain the system, set the new tank's air charge to 2 psi below cut-in while it is still empty, connect it with a relief valve, then watch a full pump cycle.[1] HomeGuide puts a typical installed replacement at $800 to $1,500.[2]
Be sure it needs replacing
A tank that has simply lost a few pounds of air doesn't need replacing, and a tank with a failed diaphragm can't be saved by adding air. The five checks sort one from the other in about fifteen minutes. In short:
| What you found | What to do |
|---|---|
| Water at the air valve | Replace — the diaphragm or bladder has failed |
| Rust, a weeping seam, a bulge, a wet base | Replace — and don't add air first |
| Air charge low again weeks after it was set | Replace |
| Air charge a little low, tank clean and fairly new | Reset the precharge and watch it |
| Tank healthy, pump still starts too often | The tank may be too small — see below |
The second row matters most. Amtrol's manual warns that adding pressure to a tank that is corroded, damaged or has lost integrity can make it burst.[1]
Choosing the new tank
- Size it from the pump
- "Same size as the old one" repeats whatever mistake was made last time. The tank has to hold enough water for the pump to run at least a minute per start; Water Well Journal's method is pump GPM × minimum run time, divided by the drawdown factor for your switch setting.[3] A 10 GPM pump on a 40/60 switch needs about 39 gallons of total volume. Run your numbers in the tank size calculator.
- Going bigger is allowed
- Amtrol's manual puts it plainly: the larger the tank, the greater the drawdown and the less the pump needs to run.[1] The limits are floor space, headroom and price.
- Check the pressure rating
- Amtrol's residential Well-X-Trol tanks are tested to 150 psig, their maximum working pressure.[1] Confirm the rating of whichever tank you choose.
- Check the connection size
- Tank connections vary by model — Amtrol's range runs from ¾ inch on small in-line tanks to 1¼ inch on large stand models.[1] A different size means a new tank tee or adapters.
- Read the warranty terms
- Amtrol's manual states that the tank must be installed by a licensed professional and that failing to follow its instructions voids the warranty.[1] If you are planning to fit one yourself, read the terms for your brand before buying.
Where it can go
Amtrol's installation requirements are a good checklist for any location:[1]
- As close as possible to the pressure switch. If the tank moves, the switch should move with it or its setting be adjusted for the pressure drop in the pipe between them.
- On a surface that can carry it full. The floor has to support the tank's operating weight, including the water.
- Away from freezing and heat. Not where temperatures fall below freezing or exceed 130 °F, and not in direct sunlight.
- Where a leak won't do damage. A drip pan connected to a drain is required if leaking or flooding could damage property.
What the installer does
Usually a job for a pro
The work combines line-voltage equipment, a pressurized system and a heavy vessel, and it has to meet local plumbing code. The sequence below is so you can follow the job and check it afterward.
- Power off, pressure off. Amtrol's instruction before any work on a tank: turn off power to the pump and release all water pressure in the tank and the pumping system.[1]
- Drain and disconnect the old tank. A waterlogged tank is far heavier than it looks. Water weighs about 8.3 pounds a gallon, so a 40-gallon tank that won't drain can hold more than 300 pounds.
- Set the new tank's precharge before it is connected. Remove the air valve cap, read the pressure, and release or add air to 2 psig below the pump's cut-in setting — 38 psig for a 40/60 switch.[1] Factory charges don't always match your switch.
- Inspect or replace the tank tee and its fittings. This is the moment to renew the pressure switch, its sensing nipple, the gauge, the relief valve and the drain valve.
- Connect the tank to the tee. Where joints are soldered, Amtrol specifies lead-free solder and flux.[1]
- Fit the relief valve. Amtrol requires one at the tank's connection to the system piping, set to open at 125 psig or more, with a discharge capacity equal to the pump's output at that pressure.[1]
- Restore power and fill. Let the pump pressurize the system until it cuts off, then check every joint for leaks.
- Run a cycle. Open a fixture until the pump starts, close it, and check the operation. Amtrol's rule for any later adjustment: only with the tank empty of water and the system off.[1]
Parts worth replacing at the same visit
| Part | Why now | Stand-alone price |
|---|---|---|
| Pressure switch and sensing nipple | Franklin lists pressure switches among the parts whose life is shortened by excessive cycling[4] | $150–$200 |
| Pressure gauge | Old gauges stick; you'll need a true reading to set the precharge | $150–$200 |
| Relief valve | Required on the tank connection; inexpensive while the tee is open | — |
| Check valve at the tank, if fitted | A leaking one causes the same short cycling as a bad tank | $150–$200 |
Prices are HomeGuide's for each part replaced on its own, including labor.[5] Done together with the tank they should cost less, because the system is already drained and the service call already paid for. We found no published price for a relief valve alone, so we don't quote one.
How to check the work
Safe to check
- Time a cycle. With a faucet running, the pump should now run at least a minute per start — Franklin Electric's minimum for its submersible motors.[4]
- Read the gauge. Cut-in and cut-out should match the switch setting, with a smooth fall between them.
- Ask for two numbers in writing: the precharge the installer set and the switch setting.
- Look for drips at every new joint the next day, and again after a week.
- Find the relief valve and make sure nothing caps its outlet.
- Test the water. The CDC recommends testing after any part of the well system is repaired or replaced.[6]
If the pump still starts every few seconds with a new, correctly charged tank, the tank was never the problem. Go back to the short-cycling decision tree — a check valve or a leak is next.
Making the new tank last
- Check the air charge once a year, with the pump off and the tank drained. Amtrol says a licensed professional should check the complete system yearly, and more often as it ages.[1]
- Amtrol notes that water quality can significantly influence a tank's life, and advises testing for corrosive elements, acidity and total solids and treating the water where needed.[1]
- Keep it dry outside: condensation and floor damp are what rust the base.
HomeGuide reports that well pressure tanks last 10 to 15 years on average.[2] Amtrol's WX models carry a seven-year limited warranty.[1]
Sources
- Amtrol. Well-X-Trol Residential Pre-Pressurized Well Tanks — Installation & Operation Instructions (WX-101 through WX-350). Accessed Sept. 28, 2026.
- HomeGuide. How Much Does It Cost to Replace a Well Pressure Tank? (article dated July 25, 2025). Accessed Oct. 8, 2026.
- Water Well Journal. Tank Selection by the Numbers — David L. Kill, PE (April 19, 2022). Accessed Sept. 28, 2026.
- Franklin Electric. Submersible Motors: Application, Installation & Maintenance (AIM) Manual, 60 Hz. Accessed Sept. 28, 2026.
- HomeGuide. How Much Does Well Pump Repair Cost? (article dated Aug. 6, 2025). Accessed Oct. 8, 2026.
- Centers for Disease Control and Prevention. Guidelines for Testing Well Water. Accessed Sept. 28, 2026.
We cite manufacturer documentation and public agencies first. Read how we choose and check sources.