What a pressure tank does and when to replace it

A pressure tank stores water under pressure so your pump does not run every time you turn on a faucet. When the tank fails — usually after 5 to 15 years depending on water quality and use — water pressure drops, the pump cycles constantly, or you lose pressure mid-shower. Replacement means draining the old tank, disconnecting the plumbing and electrical lines, removing it, and installing a new one in the same location with the same connections.

You can do this yourself if you are comfortable with basic plumbing and have the right tools, or you can hire a well technician. The job takes 2 to 4 hours for a homeowner and costs $300 to $800 in labor plus the tank itself. A new tank runs $400 to $1,200 depending on size and brand.

Key Takeaways

  • Measure your old tank or check your pump documentation to buy the correct size — tanks come in 20, 30, 42, 60, and 80-gallon models, and the wrong size will cause pressure problems.
  • Turn off power to the pump at the breaker and drain the system completely before disconnecting anything, or you will flood your basement.
  • The tank connects to the pump via a check valve and pressure switch; write down or photograph the wire connections before you disconnect them.
  • New tanks arrive empty and must be pressurized with an air compressor to match your pump's cut-in pressure before you turn the system back on.
  • If you are not confident with electrical work, hire a technician for the pressure switch reconnection — a loose wire can damage the pump.

Measure your tank size before you buy

Pressure tanks come in five standard sizes: 20, 30, 42, 60, and 80 gallons. Buying the wrong size means your pump will cycle too often (if you buy too small) or will not build pressure properly (if you buy too large). The easiest way to find your size is to look at the nameplate on your current tank — it is usually stamped on the side or top. If the nameplate is worn, measure the tank's diameter and height and call a well supplier with those numbers; they can tell you the volume.

If you cannot measure the old tank, check your pump documentation or the paperwork from your well installation. Household wells typically use 42 or 60-gallon tanks. If you have no documentation, a well technician can tell you the correct size in one visit for a service call fee (usually $75 to $150).

Turn off power and drain the system

Locate your pump's circuit breaker and switch it off. Do not skip this step — a running pump can pressurize the tank while you are working on it and cause injury. Leave the breaker off until you have finished reconnecting everything.

Next, open the lowest faucet in your house (usually a basement or outdoor spigot) and let water run until it stops. This drains the pressure tank and the lines. Open a faucet upstairs as well to break the vacuum and speed drainage. Wait 5 to 10 minutes to make sure the system is fully empty. If water continues to drip from the faucet after you think it is empty, the check valve (the one-way valve between the pump and tank) is holding pressure — this is normal and means the valve is working.

Disconnect the old tank

The pressure tank connects to the pump via three things: a water line (usually 1-inch PVC or metal pipe), a pressure gauge, and a pressure switch. Before you touch anything, take a photo of the pressure switch wires and write down which wire connects to which terminal. The terminals are usually labeled, but the photo is your backup.

Disconnect the pressure switch wires by loosening the terminal screws and sliding the wires out. Set the wires aside — do not let them touch each other or the metal tank. Unscrew the pressure gauge from the top of the tank (it usually unscrews by hand). Loosen the union nut or compression fitting where the water line connects to the tank — use two wrenches, one to hold the fitting and one to turn the nut. Once the water line is loose, you can lift the old tank out. If it is heavy, get a helper or use a hand truck.

Install the new tank and reconnect plumbing

Position the new tank in the same location as the old one. The water line connection should face the pump. Hand-tighten the union nut or compression fitting where the water line meets the tank, then use two wrenches to snug it — do not over-tighten, or you will crack the fitting. Screw the pressure gauge back onto the top of the tank by hand, then tighten it with a wrench if needed.

Before you pressurize the tank, you must charge it with air. New tanks arrive empty inside. Use an air compressor to add air through the small valve on top of the tank (it looks like a tire valve). Your pump's cut-in pressure — the pressure at which the pump turns on — is usually printed on the pressure switch or in your well documentation. Add air until the gauge on the compressor reads 2 pounds per square inch (psi) below the cut-in pressure. For example, if your pump cuts in at 30 psi, charge the tank to 28 psi. This gives the water room to compress without the pump running constantly.

Reconnect the pressure switch and turn the system on

Reconnect the pressure switch wires to the terminals in the same order you photographed them. Tighten the terminal screws firmly but do not strip them. Turn the pump breaker back on. The pump should run for 30 seconds to 2 minutes and then stop. Listen for the pump to cycle — if it runs continuously or does not run at all, turn the breaker off when ready and check your wire connections.

Once the pump stops, turn on a faucet upstairs and let water run for 30 seconds. The pressure should feel normal — not weak and not surging. If pressure is weak, the tank may not be charged correctly; turn off the pump and add more air. If pressure surges or the pump cycles every few seconds, the tank charge is too high; turn off the pump and release some air through the valve on top.

Troubleshooting after installation

If the pump will not turn on after you reconnect the pressure switch, check that both wires are fully seated in their terminals and that the terminal screws are tight. A loose wire is the most common reason a pump will not start. If the wires are tight and the pump still will not run, the pressure switch itself may be faulty — this is rare but possible if the old switch was damaged during removal.

If the pump runs but pressure is weak or drops quickly, the tank charge is usually the problem. Turn off the pump, check the air pressure in the tank with a tire gauge, and adjust it to 2 psi below your cut-in pressure. If the tank loses air pressure over time (you check it a week later and it is lower), the tank has a slow leak and must be replaced again — this is uncommon in new tanks but can happen if the tank was damaged in shipping.

When to call a technician instead

If you are not comfortable working with electrical connections, hire a technician to reconnect the pressure switch. A loose or reversed wire can damage the pump's control board and cost $500 to $1,000 to repair. If your pump is very old or your well system has unusual plumbing (multiple tanks, a bladder tank instead of a standard tank, or a submersible pump), a technician should do the work — these systems have variations that are straightforward to get wrong.

A technician will also know whether your old tank needs to be disposed of as hazardous waste (some older tanks contain asbestos insulation) and can handle that for you. If you are unsure, ask your local waste management facility before you remove the old tank.

Frequently Asked Questions

How do I know what pressure to charge the tank with?

Look at the pressure switch — it usually has two numbers printed on it, like "30/50" or "40/60". The first number is the cut-in pressure (when the pump turns on). Charge the tank to 2 psi below that number. If you cannot find the pressure switch label, check your well paperwork or call your well company.

Can I replace the tank myself if I have never done plumbing before?

Yes, if you are comfortable using two wrenches and an air compressor. The plumbing connections are straightforward — hand-tighten, then snug with wrenches. The hardest part is usually moving the old tank out and the new one in. If you are not confident, a technician can do it in 2 to 3 hours.

What if water leaks from the connection after I install the new tank?

Turn off the pump and tighten the union nut or compression fitting with two wrenches — one to hold the fitting and one to turn the nut. If it still leaks after tightening, turn off the pump, drain the system, disconnect the fitting, wrap the threads with plumber's tape, and reconnect it. Plumber's tape seals small leaks caused by thread gaps.

How often do pressure tanks need to be replaced?

Most tanks last 5 to 15 years depending on water quality and how hard your pump works. Acidic water or high iron content can corrode the inside of the tank and shorten its life. If your tank is more than 10 years old and you are having pressure problems, replacement is usually the best option.

Do I need to turn off the breaker if I am just replacing the tank?

Yes. Even though you are not working on the pump itself, the pressure switch is live electrical, and the pump can turn on unexpectedly while you are working. Turning off the breaker takes 10 seconds and prevents injury or damage.