Rainwater Tank Pump Not Working?

The toilets won’t refill, the washing machine sits there waiting for water, or the pump in the side passage is clicking on and off all night. When a rainwater tank pump stops doing its job, the whole house notices.

This guide works through the usual faults by symptom. Every check here is safe for a homeowner. Where a check would mean opening the pump, touching wiring or changing plumbing that connects to the mains water supply, the guide stops and says so.

Before you start

Water and electricity don’t mix. If the pump, its power point or the ground around it is wet from a leak or flooding, don’t touch it. Switch the pump’s circuit off at the switchboard if you can reach it from dry ground, and call for help.

Find the manual. Pumps differ. Some have a priming plug, some have a reset button on the controller, and some have neither. The manufacturer’s manual, or the label on the pump, tells you what your model allows a homeowner to do. If the manual doesn’t say you can do it, don’t.

Know what the pump feeds. Most house-connected tanks supply the toilets, the laundry cold tap and some garden taps. Many also have a rain-to-mains switching device that changes those fixtures over to mains water when the tank runs low or the pump stops.

Pump won’t turn on

Check the power. Make sure the plug is fully in and the power point is switched on. Then check the switchboard: outdoor pumps are normally on a circuit protected by a safety switch (RCD). If it has tripped, switch it back on once. If it trips again, leave it off. A safety switch that keeps tripping is telling you there is an electrical fault, often moisture in the pump or its connections, and that is a job for a licensed electrician or plumber.

Check the tank has water. Many pumps have dry-run protection that shuts them down when there is no water to draw. If the tank is empty and you have a switching device, the house should already be on mains.

Give it time after a storm or blackout. Sydney Water notes that pumps and switching devices can fail after an electrical storm or blackout.

Listen to it. If it hums but no water moves, it may have lost its prime or seized. See the note on priming below. If it makes no sound at all with power on and water in the tank, the fault is likely in the pressure switch, the controller or the motor, which are not homeowner repairs.

Pump runs non-stop or keeps cycling

A tank pump should start when you open a tank-supplied tap or a toilet refills, and stop shortly after. If it runs constantly, or starts and stops every few seconds with nothing turned on, something is asking for water.

Look for a leak first. Listen to each toilet. A cistern that keeps trickling into the pan is the classic cause, and our guide to why a toilet keeps running covers the fix. Then check the garden taps, the washing machine taps and any irrigation.

Check the suction side. Look at the pipe and fittings between the tank outlet and the pump. A small leak there can let air in, which makes the pump run on without building pressure.

If there is no leak, the likely causes are a faulty pressure switch or controller, or a pressure vessel that has lost its air charge. Both are plumber checks. Don’t leave a pump short-cycling for long: every start wears it, and a pump running dry can burn out.

Low pressure from tank-supplied taps

First work out whether it is only the tank-supplied fixtures. If the kitchen and the showers are weak too, the problem is probably on the mains side, and our water pressure service page covers the usual causes there.

Filters. A cartridge filter between the tank and the pump can clog with fine sediment and choke the flow. If your system has one and the manual shows how to change it, do so with the pump switched off.

The intake. The pump draws through a strainer, a foot valve or a floating intake inside the tank. Leaves and sludge can block it. Only check it if you can reach it without climbing on or into the tank.

The water level. A tank that is nearly empty can let the pump draw air, which drops the pressure.

If those are clear, the pump may be worn, or too small for the number of fixtures it now supplies. A switching device that is stuck part-way between tank and mains can also cause weak, uneven flow.

Noisy pump

Rattling or vibration can be as simple as the pump sitting unevenly or the mounting having worked loose. Make sure it sits level on a firm base and that nothing is touching it.

A gravelly or crackling sound usually means the pump is drawing air, from a low tank, a blocked intake or a leak on the suction side. Check those as above.

Grinding, screeching or a burning smell points to worn bearings or a failing motor. Switch the pump off at the power point or switchboard and call a professional. Don’t open the pump housing.

Switching to mains when the tank is full

If the toilets are running on mains water while the tank is full, the switching device thinks the tank is empty or the pump has stopped. As Sydney Water describes it, a mains switch changes over when the tank is low or empty, or when the pump has stopped.

So start with the pump. Check its power and safety switch, and whether it has lost its prime. If the pump is off, the switching device will keep the house on mains until it comes back.

If the pump has power and water but the house stays on mains, the switching device itself may have failed. It sits on the line between your drinking water and your tank water, usually with backflow protection, so repairing or replacing it is work for a licensed plumber.

A note on priming

A pump needs water in its casing to move water. After the tank has run dry or a pipe has been disturbed, it can lose its prime and run without pumping. Many pumps have a priming plug for this. Only prime the pump if the manual shows how, with the power off first, and never run a pump dry to “see if it catches”.

Where to stop and call a licensed professional

Stop checking and call if any of these apply:

Anything electrical. A safety switch that trips again after one reset, a burning smell, scorch marks, a damaged lead, or a fault inside the pump or controller. Electrical work is for a licensed electrician; inside the pump is for a plumber or pump technician.

Anything on the mains-connected plumbing. The switching device, the backflow protection and the pipework that joins the tank system to your drinking water supply. In NSW, plumbing work must be done by a licensed plumber, and Sydney Water says tanks connected to a toilet, washing machine or hot water system need an inspection by NSW Fair Trading, booked by the plumber.

A pump that won’t hold pressure with no leak you can find, or one that keeps short-cycling.

Leaks from the pump body or the tank itself.

And if the tank is not filling in the first place, look up at the roof: blocked gutters, screens and downpipes are a common culprit, and our gutters and downpipes checklist walks through them. Our rainwater tank plumbing service covers tank pump repairs and replacement, rain-to-mains switching devices, and connecting tanks to toilets, the laundry and garden taps.

FAQs

Why won’t my rainwater tank pump turn on?

Check that the pump has power: the plug is in, the power point is on, and the safety switch at the switchboard has not tripped. Then check there is water in the tank, because many pumps shut down to protect themselves when the tank is empty. If it hums but does not pump, it may have lost its prime. If none of these explain it, the fault is in the pump or its controller and needs a professional.

Why does my tank pump keep turning on and off?

A pump that starts and stops every few seconds with nothing turned on is usually responding to a leak on the tank-water pipework, such as a toilet cistern that keeps running or a dripping garden tap. If there is no leak, a faulty pressure switch or a pressure vessel that has lost its air charge are the usual causes, and both need a plumber.

Why is my house on mains water when the rainwater tank is full?

A rain-to-mains switching device changes over to mains when the tank is low or the pump stops. If the tank is full, the pump has usually stopped: check its power and safety switch first. If the pump has power and still is not running, or the switching device itself has failed, call a licensed plumber.