The float switch is mounted on the side of your sump pump basin, usually on a vertical rod or cable
The float switch is the part that tells your sump pump when to turn on and off. It looks like a hollow ball or bulb attached to your pump by a rod, cable, or tether. As water rises in the basin, the float rises with it. When the water reaches a certain level — usually 12 to 18 inches from the bottom — the float triggers the pump to start. When the water drains and the float drops, the pump shuts off.
On most sump pumps, the float switch hangs on the side of the basin or sits inside a separate vertical tube called a float well. The float well keeps the switch from getting tangled in the pump's intake or blocked by debris. If your pump has a tether-style float, it will be a cord attached to the pump housing with the float ball at the end, hanging freely in the water.
The exact location depends on your pump model. Submersible pumps (the kind that sit at the bottom of the basin) usually have the float mounted on the outside of the pump body or on a separate rod next to it. Pedestal pumps (which sit on top of the basin) have the float hanging down into the water on a tether or rod.
Key Takeaways
- The float switch is a hollow ball or bulb attached to your pump by a rod, cable, or tether that rises and falls with the water level.
- Most float switches are located on the side of the sump basin or inside a separate float well tube to prevent tangling.
- The float triggers the pump to start when water reaches a set level, usually 12 to 18 inches from the basin bottom.
- Submersible and pedestal pumps position their float switches differently, so check your pump's manual to find yours.
- A stuck or sluggish float switch is the most common reason a sump pump fails to turn on when water rises.
Tether-style floats hang freely in the water
A tether float is the simplest design. It is a cord or cable attached to the pump housing with a hollow ball at the end. The ball floats on the surface of the water. As water rises, the ball rises with it. When the ball reaches the trigger height, it activates a switch inside the pump housing.
Tether floats are common on pedestal pumps and some older submersible models. They are straightforward to see and check, but they can get tangled around the pump intake or caught on debris in the basin. If your float stops moving freely, the pump will not turn on even if water is rising. This is why many newer pumps use a float well instead.
Float wells keep the switch separate and protected
A float well is a vertical tube installed next to the sump basin. The float switch sits inside this tube and moves up and down as water level changes. The tube keeps the float from getting stuck on the pump intake, pipes, or other objects in the basin.
Float wells are standard on modern submersible pumps. The tube is usually 1.5 to 2 inches in diameter and extends from the bottom of the basin to above the water line. The float inside moves freely without obstruction. This design is more reliable than a tether float because nothing can tangle or block it.
If your pump has a float well, you can see the float moving inside the tube when you look at the basin. If the float is stuck at the bottom or top and does not move when you manually raise or lower the water level, the switch needs service.
Vertical rod floats mount directly to the pump housing
Some submersible pumps use a vertical rod instead of a tether or well. The rod is bolted to the side of the pump body, and the float slides up and down on the rod as water level changes. This design is rigid and does not tangle, but it requires the pump to be positioned correctly so the rod stays vertical.
Vertical rod floats are less common in residential pumps but appear on larger or commercial-grade models. They are durable and reliable if installed level. If the pump shifts or tilts, the rod may bind and the float may stick.
How to check if your float switch is working
To test your float switch, pour water slowly into the sump basin while watching the float. The float should rise smoothly as the water level climbs. When the float reaches the trigger height, you should hear the pump motor start. If the float does not move or the pump does not start, the switch is stuck or faulty.
If the float is stuck, try gently moving it by hand to see if it is physically blocked. Check for debris, mineral buildup, or corrosion around the float or inside the float well. If the float moves freely but the pump still does not start, the electrical switch inside the pump housing may be broken and will need replacement.
Never force a stuck float. If it does not move after gentle handling, stop and contact a plumber or the pump manufacturer. Forcing it can damage the switch mechanism or the pump housing.
Common problems that prevent float switches from working
A stuck float is the most common failure. Sediment, mineral deposits, and rust can build up inside the float well or around a tether float, preventing it from moving. If your pump runs constantly or never turns on, a stuck float is usually the cause.
Tangled tethers are another frequent problem. If a tether float wraps around the pump intake or gets caught on a pipe, it cannot rise to trigger the switch. This happens more often in older basins with multiple pipes or in pumps that have been running for years without maintenance.
Electrical failure inside the pump housing is less common but possible. The switch mechanism itself can corrode or fail, especially in pumps that cycle frequently or sit in very wet conditions. If the float moves freely but the pump does not respond, the internal switch is likely faulty.
Water level that never reaches the float is also a possibility. If your basin is too large or your pump is undersized, water may drain slowly enough that the float never rises to the trigger height. In this case, the float is working correctly, but the pump cannot keep up with the water entering the basin.
Where to find your pump's manual for exact float location
The best way to locate your float switch is to check your pump's manual. The manual includes a diagram showing exactly where the float is mounted on your specific model. If you do not have the manual, you can usually find it online by searching the pump brand and model number.
The model number is printed on a label attached to the pump housing or on the pump's electrical cord. Common sump pump brands include Zoeller, Wayne, Liberty, Flotec, and Superior. Each brand positions the float differently, so checking the manual saves time and prevents damage from poking around inside the basin.
If you cannot find the manual and cannot locate the float by looking at the pump, a plumber can identify it and show you where it is. Many plumbers offer free inspections or charge a small fee to diagnose why a pump is not working.
Frequently Asked Questions
What does a sump pump float switch look like?
A float switch is a hollow ball, bulb, or egg-shaped object made of plastic or foam. It is attached to the pump by a rod, cable, or tether. The float is usually white, black, or yellow and is about the size of a tennis ball to a grapefruit, depending on the pump model.
Can I replace a float switch myself?
Replacing a float switch depends on your pump type and electrical setup. Tether floats are often easier to replace because they are straightforward tied or bolted to the pump. Float wells and rod-mounted switches may require disconnecting electrical wires and removing the pump from the basin. If you are not comfortable working with electrical connections, hire a plumber.
Why is my float switch stuck at the bottom?
A float stuck at the bottom usually means sediment, mineral buildup, or debris is blocking it. Drain the basin, remove any visible debris, and gently try to move the float by hand. If it does not budge, the float well or rod may need cleaning or the float itself may have lost buoyancy and sunk.
How often should I check my float switch?
Check your float switch twice a year, ideally before heavy rain or spring snowmelt when your sump pump works hardest. Pour water into the basin and watch the float rise. If it moves smoothly and the pump starts, it is working. If it sticks or the pump does not respond, service it before the next heavy water event.
What happens if my float switch fails?
If your float switch fails, the pump will not turn on when water rises, and your basement can flood. Some pumps have a backup float or alarm to warn you, but not all. A failed float switch should be replaced or repaired as soon as you notice the pump is not responding to rising water.