Booster Pump Keeps Switching On and Off? 5 Causes and Fixes
A booster pump should only run while a tap is open. If yours cuts in every few minutes in the middle of the night, or clicks on and off while you shower, something in the system is wrong, and every unnecessary start wears the motor and the controller. These are the five usual causes.
First, which pattern do you have?
- The pump starts by itself when no taps are open: water is escaping somewhere, through a leak or back through the non-return valve (causes 1 and 2).
- The pump clicks on and off quickly while a tap is open: usually the pressure tank or the controller (causes 3 and 4).
- The pump runs, cuts out and stays off: the controller thinks it is running dry (cause 5).
1. A leak in the house
A dripping tap or a toilet cistern that keeps running lets the pressure drop, and the pump restarts to top it up, day and night. Close every tap and listen for running water. To test a toilet, put a few drops of food colouring in the cistern: if colour shows up in the bowl without flushing, the flush valve leaks.
Fix: repair the leak. The pump settles down and you stop paying for wasted water and electricity.
2. The non-return valve is leaking back
When the pump stops, a non-return valve after it holds the pressure in the house. If the valve is missing, sticky or worn, water flows back through the pump, the pressure drops and the pump starts again.
Fix: check that a non-return valve is fitted after the pump and replace it if it doesn’t seal.
3. The pressure tank has lost its air or is too small
On a pump with a pressure switch, the pressure tank stores water under pressure so small draws don’t start the pump. If the tank has lost its air charge, or is too small for the system, the pump short-cycles.
Fix: switch the pump off and drain the water from the tank. Check the air pre-charge with a tyre gauge on the tank’s valve: it should be about 0.2 bar below the pump’s cut-in pressure. Check it once or twice a year. If water comes out of the air valve, the bladder has burst; on many tanks you can replace just the bladder. A bigger tank means fewer starts: for a home booster pump, 24 to 60 litres is common, and 100 litres or more gives fewer starts and a longer pump life.
4. The flow controller is struggling
Many booster pumps use a flow controller instead of a pressure switch and tank. It switches the pump on when you open a tap and off when the flow stops. A small leak makes it cycle just like a pressure switch does, so rule out causes 1 and 2 first. A controller with a failing circuit board can also switch erratically.
Fix: replacement PC boards for the PS18L, SKD-2 and SKD-11 controllers cost far less than a new controller. If the pump starts on every tiny draw, adding a small pressure tank after the controller helps.
5. The pump thinks it is running dry
Most controllers switch the pump off if it runs without water. If yours runs, cuts out and won’t restart, the pump has most likely lost prime or the tank is empty, and the controller reads both as a dry run.
Fix: check the water level in the tank, clean the strainer, look for air leaks on the suction side, fill the pump with water and restart it.
Frequently asked questions
Is it bad if my pump keeps switching on and off?
Yes. Every start heats the motor and wears the switch. A pump on a pressure switch without a tank starts and stops every time a tap drips, which eventually burns out the motor and the switch.
Do I need a pressure tank with a flow controller?
If the pump works off a pressure switch, yes. Pumps with a flow switch or a VSD controller can run with a small tank or none at all.
What should the air pressure in my pressure tank be?
About 0.2 bar below the pump’s cut-in pressure, measured with the water drained from the tank.
How do I stop the on-off cycling for good?
Fix any leaks, keep the tank’s air charge right and choose a big enough tank. For the smoothest result, a VSD pump speeds up and slows down to hold a constant pressure instead of switching hard on and off.
Still cycling?
Send us your pump model, whether it has a pressure switch or a flow controller, and what it’s doing (a short video helps) on WhatsApp 012 881 1962. We’ll help you find the cause and the right part, with delivery anywhere in South Africa. Or browse all booster pumps.