Best Float Switches for Water Tanks, Cisterns and Sump Pits
A float switch is the small device that tells a pump when to start and stop based on water level. On well systems I use them to fill storage tanks and cisterns, to protect pumps from running dry, and to drain sump pits.
Pick the wrong type and your tank overflows or your pump runs dry. This guide explains the float switch for water tank types, how to wire pump up and pump down setups, and the switches I trust.
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| Need | Pick | |
|---|---|---|
| Best plug in tethered switch | Superior Pump 92000 | Check price |
| Best vertical switch for tight pits | Wayne 66000-WYN1 | Check price |
| Best no moving float | Little Giant RS-5LL diaphragm switch | Check price |
| Best for filling tanks and cisterns | Square D 9036 float switch | Check price |
| Best electronic level control | HydroCheck Hi-Lo pump controller | Check price |
Pump Up vs Pump Down: Get This Right First
Every float switch works in one of two directions. Getting this wrong is the most common mistake, and it is the difference between a full tank and a flooded yard.
A pump up switch is normally open when the float hangs high and closes as the water falls. A pump down switch does the opposite. Many tethered floats can be wired either way, so check the wiring diagram before you connect anything.
The Four Types of Float Switch
| Type | How it works | Best for | Watch out for |
|---|---|---|---|
| Tethered | Float swings on a cord, tether length sets the on and off gap | Wide pits, storage tanks, cisterns | Needs room to swing freely |
| Vertical | Float slides up and down a rod | Narrow sump pits | Small level range, debris can jam it |
| Diaphragm | Senses water pressure, no moving float | Pits where floats snag | Silt can block the diaphragm |
| Electronic | Probes or sensors read the level | Precise tank level control | Higher cost, needs a controller |
How to Size and Wire a Float Switch
- Check the pump’s amps. The float’s rating must exceed the pump’s running current, or the contacts will burn.
- Above about 1 HP, use a contactor. Let the float switch a contactor or relay rated for the motor, so the float only carries a small control current.
- Set the level gap. On a tethered float, a longer tether means fewer starts. Aim for at least a one minute pump run per cycle.
- Add a low level cutoff in any tank your pump draws from, so the pump stops before it can run dry.
- Fit a high level alarm on storage tanks, so an overflow never goes unnoticed.
The Best Float Switches for Water Tanks
Superior Pump 92000 Tethered Float Switch
This piggyback switch plugs between your pump and the outlet, so there is no wiring to do. It suits sump pits and simple tank setups on pumps within its amp rating.
- Type: tethered, piggyback plug
- Mode: pump down
- Install: no wiring needed
Fastest install on this list.
Pump down only, so not for filling tanks.
Wayne 66000-WYN1 Vertical Float Switch
In a narrow pit a tethered float has no room to swing. The Wayne vertical switch rides up and down a rod, so it works where other floats would snag.
- Type: vertical float
- Mode: pump down
- Best for: narrow sump pits
Reliable in tight spaces.
Shorter level range means more pump starts.
Little Giant RS-5LL Piggyback Diaphragm Switch
The RS-5LL senses water pressure through a diaphragm instead of a moving float. With nothing to tangle, it suits pits full of pipes and cords.
- Type: diaphragm, piggyback plug
- Mode: pump down
- Best for: crowded pits
Nothing to snag or tangle.
Silt can clog the diaphragm over time.
Square D 9036 Float Switch
For filling a storage tank from a well, the Square D 9036 series is an industrial standard. It mounts on the tank and can be set up to start the pump when the level falls.
- Type: tank mounted float switch
- Mode: pump up or pump down
- Best for: storage tanks, cisterns
Rugged, made for continuous duty.
Needs proper wiring, often with a contactor.
HydroCheck Hi-Lo Pump Controller
When you want precise high and low levels without a swinging float, an electronic controller does the job. The Hi-Lo uses a sensor to start and stop the pump at the levels you choose.
- Type: electronic controller
- Mode: fill or drain
- Best for: precise tank control
Accurate, no float to snag.
Costs more than a simple float.
A Typical Well and Storage Tank Setup
Low yield wells often cannot keep up with peak household demand, so many homes pump slowly into a storage tank and then use a second pump to pressurize the house. Float switches tie the whole system together.
| Where | Float job | Mode |
|---|---|---|
| Storage tank, top | Stop the well pump before the tank overflows | Pump up |
| Storage tank, bottom | Stop the house pump before it runs the tank dry | Low level cutoff |
| Storage tank, alarm | Warn you if the level gets too high or too low | Alarm only |
| Pump house or well pit | Drain flood water | Pump down |
If you are planning a storage tank, size it first with my guide to water storage tanks for well systems, then choose the floats to suit each job.
What to Look For When Buying
- Amp rating: higher than your pump’s running current
- Mode: pump up, pump down or switchable
- Cord length: long enough to reach the outlet or junction box with slack
- Potable water safe: needed for drinking water tanks
- Tether or rod length: sets how far the level moves between starts
- Warranty: one year is typical, longer is better
Float Switch Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Tank overflows | Switch wired pump down by mistake, or float stuck high | Check the mode and free the float |
| Pump never starts | Float tangled or switch failed | Clear the float, test with a meter |
| Pump starts and stops rapidly | Tether too short | Lengthen the tether for a wider gap |
| Contacts burned | Pump draws more amps than the switch rating | Fit a contactor for the motor |
| Pump runs dry | No low level cutoff in the source tank or well | Add a cutoff float or protection relay |
A Common Case: Low Yield Well, Storage Tank, Lost Pumps
A tank float stops a storage tank from overflowing, but it does nothing when the well itself runs low. On a low yield well filling a 1,500 gallon tank, the pump can run dry every day and fail every couple of years. A current sensing pump protection relay shuts the pump off when it loses water and lets the well recover, and a longer float tether gives fewer, longer runs.
For more on protecting pumps, see my guides to well pump protection devices and water storage tanks for well systems. Draining a pit? Read the best sump pumps.
Frequently Asked Questions
What is the difference between a pump up and pump down float switch?
A pump down switch turns the pump on when the water rises, for draining pits. A pump up switch turns it on when the water falls, for filling a storage tank from a well.
Can a float switch protect a well pump from running dry?
Yes. A float in the storage tank or cistern your pump draws from can cut power when the level drops too low, which protects the pump from dry running.
How do I set the on and off levels on a tethered float?
The tether length sets the gap between on and off. A longer tether gives a wider gap and fewer pump starts, while a short tether gives tighter level control.
Can a float switch run a large pump directly?
Only up to its rated amps, often around 1 HP. For bigger pumps, let the float switch a contactor or relay that carries the motor current.
Why does my float switch keep failing?
Debris, a tangled cord or a float rubbing on the tank wall are the usual causes. Give the float clear space and keep the tank clean.
