Guides

How to stop a water pump running dry

Kanari · 7 November 2026

A centrifugal transfer pump relies on the water it moves to cool and lubricate its seal. Without water it heats up fast, and a few minutes of dry running can ruin the seal or the impeller. These are the ways to make sure it never happens.

1. Keep a stop level above the intake

Set the stop level well above the point where the intake starts drawing air. If your pump sputters when the cistern is at 15%, stop it at 25%. Whirlpools near the intake suck air before the tank looks empty.

2. A float switch in the cistern

A float switch wired into the pump's control circuit cuts the power when the water falls below it. It's simple and works without the internet. Fit it with its own cable to the panel, and test it the way its manual describes, usually by letting the float drop as if the tank were empty and checking the pump stops.

3. Watch the pump's power

A pump moving water draws a steady amount of power. When it loses its water, the power drops noticeably. A smart switch that measures power can stop the pump when the reading falls below a threshold for a minute or two. This also catches a blocked foot valve or a closed suction valve, which a float switch can't.

4. A safety timer on the switch itself

If the pumps are controlled over the internet, the switch should turn itself off if it stops hearing from the system, for example after ten minutes. Then a lost connection doesn't leave a pump running unwatched.

Bigger pumps need a contactor

Motors draw a surge when they start. Unless a smart switch is rated for motor loads at your pump's size, have it drive the coil of a motor-rated contactor instead of carrying the pump current itself, with a circuit breaker upstream. As a rough guide this matters above about 1.5 kW; an electrician should check the ratings on both.

Kanari's pump switch uses the stop level, the power reading and the safety timer together. See the pump switch.