How well pump replacement works

What actually happens between calling a contractor and having water again: how the pump type gets chosen, what removal and installation involve, and why the well needs disinfecting afterward.

Replacing a well pump follows the same sequence no matter who does the work: match the pump type to the well before anything is disconnected, remove the failed pump, install and connect the new one, then disinfect the well and test the water before calling it finished. What differs most is how much of that sequence happens above ground and how much happens down the borehole, and that depends entirely on which kind of pump the well needs.

For what this costs, see well pump replacement cost. For whether replacing is the right call in the first place, see well pump repair or replace.

How the pump type gets chosen

The well decides the pump type, not the homeowner. A contractor confirms the well's depth and required flow before ordering parts, because a pump rated for the wrong depth either fails to deliver water or wastes capacity the property will never use.

The published depth and lift-height ranges for the three pump types overlap rather than landing on one clean number, and reconciling exactly which figures apply where is its own topic: see submersible vs. jet pump depth for every published range and where they cross over. What matters for the replacement job itself is simpler: whichever type the well needs, the new pump goes in at the same type and the same depth as the one it replaces.

Pulling the old pump

On a submersible system, most of the physical job is pulling the drop pipe, the electrical cable and the pump itself up out of the casing in sections once the well cap is off, then coiling wire and pipe as it comes. Whatever sits at the top, the control box and the pressure switch, gets inspected at the same time since it is already exposed.

None of that applies to a shallow-well jet pump. The pump sits above ground near the pressure tank, so removal means disconnecting fittings and wiring in the equipment room rather than extracting anything from the well. For why that difference changes the repair-versus-replace math and not just the physical job, see the factor the cost tables miss.

Installing the new pump

The new pump goes in at the same depth as the old one. On a submersible system the pipe, wire and pump go back down together, the wellhead gets sealed, and the system runs through a few on and off cycles while the installer checks that pressure builds and holds. On a shallow-well jet pump the new unit connects to the same fittings already in the equipment room, and pressure calibration happens right there instead of down a borehole.

Either way, running the pump before disinfecting the well confirms the pump itself is working before anything else gets blamed on it.

Does a well need to be disinfected after a pump replacement?

Yes, according to Missouri's Department of Natural Resources, whose published guidance covers wells in that state: "Disinfection is needed when a water sample tests positive for bacteria, the well has been impacted by floodwater, or when work on the well (e.g., a pump replacement or liner installation) has been completed." A pump replacement is one of three triggers the guidance names, alongside a positive bacteria test and flood impact.

Source: Missouri Department of Natural Resources, Disinfecting Your Water Well, PUB2733

How soon can you test the water after disinfection?

Not immediately. The same Missouri DNR guidance states: "Wait 5-10 days after disinfection to collect the sample. Waiting allows any residual chlorine to be flushed from the water system." It continues: "If the sample is positive for total coliform, repeat the disinfection process." And it adds: "Do not be alarmed if multiple disinfections are needed to clean a water system as sometimes the bacteria have been growing for a period of time and require several disinfections."

Source: Missouri Department of Natural Resources, Disinfecting Your Water Well, PUB2733

Who performs the disinfection

Missouri's guidance states, under "Before you begin": "We recommend using a licensed well contractor to perform the disinfection procedure." It also states: "However, if you must perform the procedure yourself please use the following instructions," and gives a full homeowner procedure rather than treating this as contractor-only work.

Well systems combine electricity and pressurised water, and getting either wrong is dangerous. See the safety checks in well pump troubleshooting checklist before working on any part of the system yourself.

If the pump or the pressure tank is still an open question, signs a well pump is failing walks through the difference before you book anyone.

Source: Missouri Department of Natural Resources, Disinfecting Your Water Well, PUB2733

What this costs, and whether replacing is right

None of the above prices the job. Well pump replacement cost sets out the published national figures by pump type and the components priced separately. If the question is still whether a repair would do instead, well pump repair or replace sets the published repair and replacement costs against each other and shows where they cross over.