Rainwater tank pump keeps turning on and off
If your rainwater tank pump keeps turning on and off, you’re not alone. This is one of the most common water pump issues we see across Brisbane homes. In most cases, the pump either needs replacing or there’s a water leak somewhere in the line, Often around the outlet or inside the pump itself.
At Plumbologist Brisbane, we’ve repaired and replaced hundreds of rainwater pumps across South Brisbane, Logan, Redlands, and Ipswich. Below, we’ll walk you through why your rainwater tank pump keeps turning on and off, what you can do to check for leaks, and when it’s time to call a licensed plumber.
Quick Answer
When your rainwater tank pump keeps turning on and off, it’s typically caused by:
A leaking outlet or pipe joint
A damaged pump diaphragm or non return valve
A faulty pressure switch
Or the pump nearing the end of its life
If you notice the pump cycling frequently, Even when no taps are running. It’s almost always due to a small air or water leak in the system.
Understanding How a Rainwater Tank Pump Works
Before we fix the problem, it helps to know how the system operates. A rainwater tank pump automatically turns on when it detects a drop in pressure (when you open a tap) and turns off once the pressure stabilizes.
If your rainwater tank pump keeps turning on and off, it means pressure is dropping somewhere, Often because the pump thinks water is being used when it isn’t.
A typical Brisbane setup includes:
A pump unit connected to the tank outlet
Suction line drawing water from the tank
Outlet line feeding to irrigation, toilets, or washing machines
A non return valve to stop water flowing back
When any part leaks, even slightly, the system loses pressure and the pump cycles repeatedly.
Common Reasons Your Rainwater Tank Pump Keeps Turning On and Off
1. Leaking Outlet or Pipework
The most frequent cause when your rainwater tank pump keeps turning on and off is a leak on the outlet side.
Check for:
Damp patches near fittings
Drips under connections
Hairline cracks on PVC elbows
Water trails around the pump housing
Even a tiny leak can cause pressure loss and trigger the pump every few seconds.
2. Internal Pump Leaks
If no external leaks are visible, the issue could be inside the pump itself.
Common internal faults include:
A worn seal or diaphragm
A cracked casing
A leaking check valve
In many cases, once internal leaks start, the pump needs replacement.
Plumbologist technicians often replace pumps that have cycled excessively or show corrosion especially older brands not built for constant cycling.
3. Faulty Pressure Switch
A failing pressure switch can misread pressure levels and cause the rainwater tank pump to keep turning on and off.
This can happen after years of exposure to moisture and dirt, or if the switch contacts are worn out. While some switches can be replaced, it’s often more cost effective to install a new pump assembly that includes a modern controller.
4. Air Leaks in the Suction Line
If air gets into the system, the pump may lose prime and cycle repeatedly.
Typical signs:
Gurgling noises from the pump
Water spurting from outlets
Visible air bubbles in clear hose sections
Seal all fittings with plumber’s tape and make sure suction hoses are airtight.
5. Non Return Valve Failure
The non return valve (check valve) keeps water from flowing backward into the tank. If it fails, pressure drops when the pump shuts off causing it to restart over and over.
A quick test: Turn off power to the pump. If pressure drops and the outlet flow weakens within seconds, the valve isn’t holding pressure.
How to Troubleshoot Step by Step
Here’s how to check what’s wrong when your rainwater tank pump keeps turning on and off:
Turn off all water outlets
Make sure no toilets, washing machines, or garden taps are using water.Listen to the pump
If it turns on without any demand, you’ve confirmed a leak or pressure issue.Inspect all fittings and joints
Look for dampness or slow drips even minor leaks cause cycling.Check the outlet line
Disconnect it temporarily to see if water continues to leak out.Test the check valve
Remove and inspect it for dirt or corrosion.Power down and check internal parts
Remove the cover and inspect seals and diaphragms for wear.
If you’re still unsure, it’s best to call Plumbologist Brisbane for a full inspection. We can pressure test your system and pinpoint whether the rainwater tank pump needs replacing or if it’s a minor leak repair.
When to Replace the Pump
If your rainwater tank pump keeps turning on and off even after checking for leaks, replacement might be the only long term solution.
Typical signs it’s time to replace:
Pump is over 5 years old
Motor is noisy or overheating
Frequent tripping or cycling
Low water pressure at outlets
At Plumbologist, we use Australian standard rainwater pumps from brands like Davey, Onga, and Grundfos, all known for reliability in Queensland’s weather.
Brisbane Conditions and Your Pump
Brisbane’s subtropical climate puts extra stress on outdoor water systems.
Factors that contribute to failure include:
UV exposure degrading seals
Heavy rainfall causing overflows
Sediment buildup from roof debris entering the tank
Frequent start-stop cycles from irrigation timers
If your rainwater tank pump keeps turning on and off during or after rain, sediment might have clogged the valve or pressure switch. Cleaning and servicing the unit once a year can prevent this.
Why a Leak in the Outlet Is Most Common
In Brisbane homes, the outlet line leak is the #1 cause when your rainwater tank pump keeps turning on and off.
Over time, PVC or flexible hose connections expand and contract with temperature, loosening seals. Even a slow drip can trigger constant cycling.
The good news? These leaks are inexpensive to fix, Usually by tightening or replacing a fitting.
Professional Diagnosis from Plumbologist Brisbane
If you’ve run through all the steps and your rainwater tank pump keeps turning on and off, it’s time for a licensed plumber to inspect it.
Our qualified team provides:
On-site leak detection
Pump testing and diagnostics
Replacement with energy efficient models
12-month workmanship guarantee
We service all Brisbane suburbs from Mount Gravatt to Wynnum, Loganholme to Forest Lake and we’re available for same day emergency pump repairs.
We proudly service:
Brisbane Southside: Mount Gravatt, Holland Park, Rochedale
Logan City: Beenleigh, Daisy Hill, Meadowbrook
Redlands: Capalaba, Victoria Point, Cleveland
Inner Brisbane: Camp Hill, Coorparoo, Greenslopes
Our Google My Business profile: Plumbologist Brisbane
Pro Tip: Install a Pump Cover
To extend your pump’s life:
Protect it from sun and rain with a ventilated cover
Keep it elevated to avoid water pooling
Clean filters every 3 months
This helps prevent future cycling problems and reduces wear on seals.
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