Everything You Need to Know About Mechanical Float Switches
Quick answer: A float switch turns your pump on when the water rises and off when it drops. If your pump no longer works automatically, lift the float by hand: if the pump starts, the float is stuck or incorrectly adjusted. If nothing happens, the switch or pump is defective.
How does a float switch work?
A float switch consists of a float with a switch inside or attached to it. As the water rises, the float rises or tilts. At the turn-on point, the switch makes contact and the pump starts. When the water drops to the turn-off point, the float drops back and the pump stops. The difference between these two points is called the switching height.
Types of float switches
| Type | How it works | Suitable for |
|---|---|---|
| Float on the pump (arm) | Float on a hinged arm on the pump housing | Compact sumps, clean to lightly contaminated water |
| Cable float (tilt float) | Ball on cable tilts; cable length determines switching height | Spacious sumps, dirty water, construction |
| Vertical float | Float slides along a rod | Narrow sumps with limited space |
| Electronic sensor | Electrodes detect water, no moving parts | Very narrow sumps, switches at a few mm |
Properly adjusting a float
- Ensure free space. The float must not touch the pit wall, pipes, or cables. Otherwise, it will get stuck.
- Set the switching height wide enough. Too small a difference between turning on and off will cause the pump to constantly cycle (pendulum effect). This wears out the motor and switch.
- Position the turn-off point above the inlet. This prevents the pump from drawing air and keeps the motor cooled.
- Install a check valve. If water from the discharge pipe flows back into the pit, the pump will immediately restart.
- Test: fill the pit or lift the float and check if the pump starts and stops at the correct level.
Common malfunctions
| Problem | Cause | Solution |
|---|---|---|
| Pump does not start | Float is stuck or defective | Free and test float; otherwise replace |
| Pump does not stop | Float remains in the high position | Clear space around the float, remove debris |
| Pump constantly cycles on and off | Switching height too small or water flows back | Increase switching height, install check valve |
| Pump runs dry | Turn-off point too low | Adjust float higher |
| GFCI trips | Moisture in float cable or switch | Have float or pump inspected/replaced |
Also read: 6 common water pump problems and how to fix them yourself.
Maintenance
Check a float twice a year: clean the float, remove dirt, grease, and fibers from the pit, and lift the float to test if the pump starts. Also check if the cable is not damaged or kinked. A float that has not moved for years can get stuck when you need it.
Extra certainty? A float does not warn if it fails. For an important basement or pump pit, a high water alarm is cheap insurance.
Replacing a float or pump
If only the float is broken, you can replace it separately. If the pump is also old or the float is built-in, a new pump with a float is often the smartest choice.
UNIVERSAL – EVERY 230V PUMP
RP CRAB float (universal)
Electronic sensor with plug connector, cannot get stuck.
€99.50
View float
ORIGINAL HOMA PART
HOMA float switch C(H)140/150
Replacement float for the HOMA Bully C(H)140 and C(H)150 WA.
€56.95
View float
NEW PUMP WITH FLOAT
HOMA Bully C 140 WA
Robust cellar pump with built-in float switch.
€366.95
View pumpView all loose floats or read which type of float suits your situation.
Frequently asked questions
How do I test a float switch?
Lift the float by hand while the pump is connected. If the pump starts, the switch is working. If nothing happens, check the power and cable; if they work, then the float or pump is defective.
Why does my pump keep cycling on and off?
Usually, the switching height is too small or water flows back into the pit from the discharge pipe. Increase the switching height and install a check valve.
Can I replace a float separately?
Yes, for most pumps. A universal sensor with a plug connector, like the RP CRAB, works on any 230V submersible pump.
Which float fits in a narrow pit?
A vertical float or an electronic sensor. A cable float requires too much space to tilt.
Unsure which pump fits?
Don't know which float fits your pump? Send a photo of the nameplate and we'll find out for you.
Ask for free adviceView loose floats
1 comment
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