Submersible pump with or without a float switch?
David MeijerQuick answer: if the pump is permanently installed in a pit, basement or crawl space, choose a pump with a float switch: it switches itself on and off and cannot run dry. If you use the pump only occasionally and stay with it (emptying a pond, an emergency), a pump without a float switch is enough. For tight pits or very low water levels, choose an electronic sensor.
→ Go straight to: recommended pumps with and without a float switch
What does a float switch do?
A float switch is a level switch. When the water rises to a certain point, it switches the pump on; once the water has been pumped away, it switches it off again. That way you don't have to keep an eye on the pump, and you prevent it from running dry. Most submersible pumps are cooled by the water itself; without water, the motor overheats.
With or without a float switch: the difference
| With float switch (automatic) | Without float switch (manual) | |
|---|---|---|
| Ideal for | Permanent installation: pump pit, basement, crawl space, rainwater tank | Temporary use: pond, swimming pool, excavation, emergency |
| Running dry | Prevented: the pump stops by itself | Risk: you have to switch it off yourself |
| Supervision | Not needed | Needed (or a timer switch) |
| Pumping down low | The float switch stops at a set level | Keeps pumping until the pump draws air |
What types of float switch are there?
1. Mechanical float switch (on the pump)
A float on an arm attached to the pump operates a switch. Simple, affordable and reliable in clean to lightly contaminated water. Drawback: it needs room to move and can get stuck due to dirt or fibres. Example: the HOMA Bully C 140 WA.
2. Cable float switch (electromechanical)
The switch sits inside a floating ball on a cable. By changing the cable length, you set when the pump starts. Less sensitive to dirt, but the pit must be wide enough for the ball to move freely. Widely used on wastewater and construction pumps.
3. Electronic sensor (electrodes)
Two electrodes detect whether water is present. No moving parts, so ideal for tight pits and for switching at just a few millimetres of water. A separate sensor such as the RP CRAB float switch turns any 230V pump into an automatic pump: you plug the pump into the sensor's piggyback plug.
Already have a pump without a float switch? You don't need to buy a new pump: a separate float switch or level switch makes it automatic.
Which float switch should I choose for my situation?
| Situation | Recommendation |
|---|---|
| Spacious pump pit or basement, clean water | Mechanical float switch on the pump |
| Dirty water or excavation | Cable float switch (less sensitive to dirt) |
| Narrow pit (< 30 cm) | Electronic sensor |
| Floor as dry as possible | Flat suction pump with sensor (switches at a few mm) |
| Automating an existing pump | Separate sensor with piggyback plug |
Pump without a float switch? Keep this in mind
A pump without a float switch keeps running until you pull the plug. Stay nearby and switch it off as soon as the water is gone. Never let a pump with a top outlet run dry for long: it is cooled by the water. Pumps with jacket cooling cope with this better.
Recommended pumps
WITH MECHANICAL FLOAT SWITCH
HOMA Bully C 140 WA
Robust German quality pump for basements and pump pits, plug & play.
View current price
WITH SENSOR – FLAT SUCTION
Simer 6 + CRAB float switch
Switches on at just a few mm of water and pumps the floor almost dry.
View current priceWITHOUT FLOAT SWITCH
Pentair Simer 6
For temporary use: flat suction down to 2 mm, with a built-in check valve.
View current priceOnly need the float switch? See the RP CRAB float switch or all separate float switches.
Frequently asked questions
Do I need a submersible pump with a float switch?
Yes, if the pump is permanently installed in a pit, basement or crawl space and has to work on its own. For temporary use where you stay with the pump, a pump without a float switch is enough.
Can I add a float switch to an existing submersible pump?
Yes. A separate level switch with a piggyback plug, such as the RP CRAB, makes any 230V submersible pump automatic.
Which float switch fits in a narrow pit?
An electronic sensor. Unlike a mechanical or cable float switch, it needs no room to move.
What happens if a submersible pump runs dry?
Most submersible pumps are cooled by the water. If the pump runs dry, the motor overheats and can be damaged.
Not sure which pump is right?
Tell us how big your pit is and what kind of water you are pumping. We will advise you free of charge on which pump and float switch fit.
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