The float switch on a sump pump is the device that turns on the pump automatically when the water level in the sump basin rises. Without the float switch to tell the system to start pumping, your sump basin would fill with water without your knowing, eventually flooding the basement. Using a float switch on your pump allows your sump pump system to turn on automatically, ensuring your home is protected even when you’re away or asleep.
How Does a Sump Pump Float Switch Work?
The float switch sits inside your sump basin, either on the surface of or submerged in the water. As the water level rises, the switch is triggered, turning on the pump so it can pump water up and out of the basement. When the water level subsides, the switch goes dormant, waiting for the next water level increase to trigger the process again.
Three Types of Sump Pump Float Switches
There are three types of float switches available for sump pump systems. It’s important to choose the right one for your setup — the switch is often the first part of the waterproofing system to fail, but you can reduce the risk of failure by selecting the switch that’s best for your setup. Also worth noting: Some sump pumps come with integrated — i.e., built-in — switches.
Tethered float switch
Sometimes called a “horizontal float switch,” this type of switch floats freely on the surface of the water in the sump basin, attached to the sump pump by a chain or floating arm. As the water level rises, the tethered switch rises with it, activating the sump pump. Relatively inexpensive, this type of switch can also be unreliable — it can snag on the basin liner, debris, or another part of the system, causing it to fail. If your sump basin is small or crowded, this design may not work for your system.
Vertical float switch
Similar to the tethered float switch, the vertical float switch rises as the water level rises, activating the sump pump. The key difference here is that the vertical float switch is mounted on vertical rods, which keep it from roaming freely about the basin and getting snagged on other equipment. This makes these switches more reliable than tethered switches, though they are generally no more expensive, making them an excellent choice for most homeowners, even those with small sump basins.
Diaphragm switch or pressure switch
Rather than floating in the sump basin, these switches sit on the bottom. As the amount of water in the basin increases, the weight of the water compresses these switches, activating the sump pump. These switches tend to be highly reliable, but they’re also more expensive than the other two designs.
These videos cover the differences among different styles of float switch and offer tips for choosing the right switch for your system:
How Do I Know if My Sump Pump Float Switch Is Bad?
While sump pump float switches are fairly straightforward mechanisms, they can and do fail. They can snag on the pump or the basin, get clogged or pinned down by debris, or simply suffer a mechanical or electrical failure.
If your basement floods, you’ll want to know why — here’s how to test your sump pump float switch:
You can test any style of switch — tethered, vertical, or diaphragm — most easily by pouring water into the sump basin to trigger the switch and, one would hope, cause the pump to turn on. For a vertical or tethered switch, you can also raise the switch by hand to see whether it turns on the pump. Whichever testing method you choose, if the level is high enough but the pump doesn’t turn on, you might have a bad switch.
Investigate further by using a continuity tester on the switch lead wires to confirm that the switch, rather than another component in your system, is what’s broken.
How Can I Adjust a Sump Pump Float Switch?
If your sump pump is running too frequently, or not at all, and you’ve ruled out other problems such as the check valve, you might need to adjust the float switch.
The type of float switch you’re using determines the correct approach when adjusting the switch. Regardless of which design you’re working with, begin by turning off the power to the system to prevent injury.
If yours is a tethered or horizontal float switch, you might need to simply move it to a different location in the basin or adjust the maximum water level by shortening or lengthening the cord connecting it to the pivot point.
Vertical float switches can be adjusted by disconnecting the connector holding the rod and adjusting the float up or down as needed.
Diaphragm or pressure switches should need no adjustment, but check periodically to keep the switch clear of debris and ensure that it’s in the desired location. (The action of the pump can cause items to shift around in the basin.)
After adjusting the switch, plug in the pump and test the setup by filling the basin with water until the pump turns on.
How to Replace Your Sump Pump Float Switch
Though sump pump float switches are generally reliable if well installed and maintained, they are the system component most likely to fail.
Fortunately, they’re also relatively inexpensive and easy to replace. The least expensive design, the tethered float switch, can usually be bought for about $25; the most expensive, the diaphragm/pressure switch, may run over $100.
Before You Begin: Gather the Correct Parts
Materials needed for this project depend on the style of switch you purchased; consult manufacturer directions to determine. In general, you will need the sump pump float switch, a screwdriver, waterproof glue, sealant, and possibly zip ties.
Here are three videos that provide a good overview of the replacement process:
Step 1: Drain the Sump Pump Basin.
If possible, drain water from the sump pump basin or pit. Turn off electricity to the system, and secure cords and wires away from standing water.
Step 2: Determine Positioning and Adjust the Tether Length/Float Height.
If installing a tethered or vertical float switch, determine the best place to connect it and the length of the tether or the ideal height for the float. The switch should hang a few inches above the top of the sump pump motor, though the optimal height will vary depending on the size of your basin and the power of the motor. The goal is to hang the switch at a height that allows plenty of time for the system to do its job before flooding becomes critical, without causing the pump to run too often. For many systems, the proper height triggers the pump when water in the basin rises by about 5 inches.
Install the switch following manufacturer instructions.
Step 3: Test the Switch.
Plug in the sump pump and turn it back on. Pour water into the sump basin until the pump switches on and begins pumping water.
Pay attention to the water level at which the pump turns on, and make further adjustments if needed. When you’re satisfied that the switch is properly positioned to protect your basement from flooding, congratulations! You have successfully installed a sump pump float switch.
How to Maintain Your Float Switch
Ideally, your float switch should require little to no maintenance. Pay attention to the overall performance of the system, adjust the switch if the pump isn’t turning on soon enough (or turning on too often), and take care to remove debris (if any exists) from the basin periodically.