If water overflows from your purifier’s storage tank, drips out of the cabinet, or the pump keeps running even when the tank is full, the part that is supposed to sense a full tank has usually failed. In most domestic purifiers that is a float valve or a float switch.
Float valve vs float switch – what’s the difference?
| Part | How it works | Where it is used |
|---|---|---|
| Float valve (FLV) | A mechanical valve with a floating arm. When water rises, the float lifts and physically shuts the water inlet to the tank. | Storage tanks of many cabinet-type purifiers |
| Float switch | An electrical switch inside a float. When the tank is full it cuts power to the pump and solenoid valve. | Purifiers with an electrical tank-full cut-off |
Some purifiers have both. Either one failing can cause overflow or a pump that never stops.
Common causes of overflow
- Float stuck in the down position because of scaling, dirt or a misaligned arm.
- Worn rubber seal in the float valve, so it cannot shut completely.
- Float switch contacts failed – the pump keeps getting power.
- Solenoid valve stuck open – water keeps entering even after the pump stops.
- Loose or cracked tank cover that lets the float sit at the wrong height.
How to check and fix
- Unplug the purifier and close the inlet.
- Open the tank cover and lift the float by hand – it should move freely up and down.
- Clean white scaling or dirt from the float and its hinge with a soft cloth.
- Check the rubber seal at the tip of the float valve. If it is torn or hard, replace the valve.
- For a float switch: with the float lifted up, the pump should stop. If it keeps running, the switch is faulty.
- Reassemble, open the inlet, and watch one full cycle until the tank fills and the flow stops.
Replacement parts
- Float valve / float switch
- Solenoid valve – check this too if water keeps entering
- Storage tanks – if the tank itself is cracked
Don’t ignore an overflow
Continuous overflow wastes a lot of water, can damage your kitchen cabinet and floor, and keeps the pump running for long hours, which shortens its life.
Frequently asked questions
Why does water leak from the bottom of my RO?
Common reasons are tank overflow, a loose push-fit pipe, or a cracked housing. Check the tank level first.
Why does my RO pump never stop?
The tank-full signal is not reaching the pump – usually a float switch or high-pressure switch fault, or a leak that keeps the tank from filling.
Can I fix a float valve myself?
Yes. Cleaning or replacing a float valve is simple and needs no special tools.
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