What a submersible pump does and how to set it up

A submersible pump sits underwater in your sump pit and pushes water out of your basement through a discharge pipe. Unlike a pedestal pump that sits on the floor beside the pit, a submersible pump is sealed and waterproof — the motor and pump are one unit that lives in the water. To set one up, you place it in the bottom of your sump pit, attach a discharge pipe to the outlet, and plug it in. The pump turns on automatically when water rises to a certain level, thanks to a float switch or pressure sensor inside.

Before you install one, measure your sump pit's depth and diameter so you buy a pump that fits. Most residential submersible pumps are 3 to 4 inches wide and need at least 18 to 24 inches of clearance above the bottom of the pit. Check the pump's horsepower rating — 1/3 to 1/2 horsepower is standard for basements that get moderate water intrusion. Read the manufacturer's manual for your specific model, because set up levels and discharge pipe sizes vary.

Key Takeaways

  • A submersible pump sits in the water at the bottom of your sump pit and automatically turns on when water rises to the float switch level.
  • The discharge pipe must slope downward away from your house and drain at least 10 feet away, or water will seep back into the pit.
  • Check the pump and pit monthly during wet seasons by pouring water in to make sure the float moves freely and the pump starts.
  • A backup power source or battery backup system protects you if the power goes out during heavy rain.
  • Most submersible pumps last 5 to 10 years before the seal fails and water enters the motor housing.

Installing the discharge pipe correctly

The discharge pipe is where most people make mistakes. Water pumped out of your basement will flow back down into the pit if the pipe is not sloped correctly or if it drains too close to your foundation. The pipe must slope downward continuously from the pump outlet all the way to the exit point — no flat sections where water can pool. Use PVC or rigid plastic pipe, not flexible hose, because flexible hose can kink and trap water.

The discharge point must be at least 10 feet away from your foundation, and farther is better. If you have a basement window well or crawlspace vent nearby, aim for 15 to 20 feet. In winter, the discharge should drain to a dry well, a French drain, or a storm drain — never let it pool on the surface where it can freeze and back up into the pit. If you live in a cold climate, some people install a check valve in the discharge line to prevent backflow when the pump is off.

How the float switch and automatic set up work

Most submersible pumps use a float switch — a hollow ball attached to a rod or cable that rises and falls with the water level. When water reaches a certain height, the float rises and triggers a switch that turns the pump on. As the pump drains the pit, the float drops, and when it reaches the off level, the switch cuts power and the pump stops. This cycle repeats automatically whenever water enters the pit.

Some newer pumps use a pressure sensor instead of a float. The sensor detects water pressure at the bottom of the pit and turns the pump on and off based on depth rather than a mechanical float. Pressure sensors are more reliable in pits with a lot of sediment, because they do not get stuck the way a float can. Check your pump's manual to see which type you have, because the maintenance steps are slightly different.

Testing the pump and keeping it running

Once a month during spring and fall — when your basement is most likely to get water — pour a bucket of water into the sump pit and watch what happens. The float should rise smoothly, the pump should start within a few seconds, and water should drain out the discharge pipe. If the pump does not start, the float may be stuck against the pit wall, or the power cord may be loose. If water drains slowly, the discharge pipe may be kinked or clogged.

Keep the pit clean by removing leaves, dirt, and debris that fall in. A clogged pit can trap the float or cause sediment to jam the pump intake. If your pit has a cover, make sure it fits loosely enough that the float can move — a tight cover will prevent the pump from activating. Once a year, especially before heavy rain season, unplug the pump and inspect the intake screen for debris. If you see cracks in the pump housing or water leaking from the motor, the seal has failed and the pump needs to be replaced.

What to do when the power goes out

A submersible pump stops working the moment the power cuts out, and heavy rain during a storm can flood your basement in hours. If you live in an area with frequent power outages or heavy rainfall, a battery backup system is worth the investment. These systems include a separate pump powered by a rechargeable battery that activates when the main power fails. The battery pump is smaller and slower than the main pump, but it can handle moderate water for several hours.

Battery backup systems cost between $500 and $2,000 installed, depending on the pump size and battery capacity. They need to be charged regularly and tested every few months to make sure the battery still holds a charge. An alternative is a portable generator that you can plug the pump into during an outage, but this requires you to be home and awake to set it up. Some people use both — a battery backup for the first few hours, and a generator if the outage lasts longer.

Signs your submersible pump is failing

Submersible pumps typically last 5 to 10 years before the seal around the motor fails and water seeps inside. Once water enters the motor housing, the pump will short out and stop working. Watch for these warning signs: the pump runs but drains water very slowly, the pump cycles on and off more frequently than it used to, or you hear grinding or squealing noises coming from the pit. Any of these means the pump is near the end of its life.

If water is leaking from the pump housing itself — not from the discharge pipe — the seal has failed and the pump cannot be repaired. You will need to replace it. Before you buy a new pump, turn off the old one and let the pit drain completely, then measure the pit again to make sure the new pump will fit. If the pit has become shallower due to sediment buildup, you may need to clean it out before installing the replacement pump.

Frequently Asked Questions

Can I use a submersible pump without a discharge pipe?

No. Without a discharge pipe, water pumped out of the pit will straightforward flow back down into it, and the pump will run continuously without draining anything. The discharge pipe must slope downward and exit at least 10 feet away from your foundation.

What happens if the float switch gets stuck?

If the float gets stuck in the up position, the pump will run continuously and may overheat. If it gets stuck in the down position, the pump will not turn on even when water rises. Gently move the float by hand to free it, or remove debris from the pit that may be blocking it. If it stays stuck, the float mechanism needs to be replaced.

Do I need a check valve in the discharge pipe?

A check valve prevents water from flowing backward into the pit when the pump is off. In cold climates, a check valve stops water in the discharge pipe from freezing and backing up. In warm climates, it is optional but recommended to reduce the number of pump cycles.

How often should I replace a submersible pump?

Most submersible pumps last 5 to 10 years depending on how often they run and how much sediment is in the pit. If your basement gets water frequently, the pump will wear out faster. Replace it as soon as you notice it draining slowly or cycling on and off more than usual.

Can I install a submersible pump myself?

If you are comfortable with basic plumbing and electrical work, you can install one. You will need to cut and fit PVC pipe, attach it securely, and plug the pump into a GFCI outlet. If you are unsure about any step, call a plumber — a poorly installed discharge pipe can cause water to back up into your basement.