Tank Pump Not Working? Why it Keeps Cycling On and Off, and When to Repair or Replace It

If you’ve found that the water tank pump keeps switching itself on and off, even when no taps are running, it’s usually a sign something in the system needs attention. This is commonly called short-cycling, and it puts extra strain on the pump every time it kicks in and out, wearing down parts that would otherwise last for years.

The tricky part is that short-cycling can come from a handful of different causes, some simple to fix, others pointing to a pump that’s on its last legs. This is a common issue for Melbourne properties running tank-fed water systems, and knowing the difference matters , because a quick repair might solve the problem for a fraction of the cost of a full replacement.

With this in mind, here’s what’s actually going on when your pump won’t stop cycling, and how to tell whether it needs a repair or a replacement.

Why Your Water Tank Pump Keeps Cycling On and Off

Here are the common causes of the cycling issue, along with how you can fix each one.

Common causes of cycling include:

• > Leaking Pipes. If you have a dripping tap or a toilet that is always running, this can lower the system pressure, which has the pump turning on and off repeatedly.

• > Waterlogged Pressure Tan Your pump has an air bladder inside to help maintain internal pressure. When you turn the tap on, the air pressure pushes the water out through the pipes. If it has been ruptured or has lost its air charge, the air bladder can’t function, and this engages the water pump.

• > Faulty Pressure Switch. Wear and tear, dirty connections or just incorrect settings can prevent the pressure switch from reading the pressure accurately.

• > Stuck Check Valve. This is a one-way mechanical gate that allows water to flow in one direction along your pipes. If it isn’t working properly it can let water back down the pipe, causing a pressure drop, engaging the tank pump.

• > Suction Line Air Leaks. Worn pipes, or if there are cracks in the tubing, can allow air to get in, which makes the pump lose prime. This causes the pump to engage to make up for the pressure drop.

How to Check Your System

It’s quite easy to check your system to see if there are any problems, and what they are.

1. Turn off all the taps in your house. Any appliances that use them, just turn them off.
2. Listen to the pump. If it is still running, or if there are clicks as it turns on and off, you have a pressure problem, or a leak.
3. Inspect all the pipes and joints, looking for slow drips or wet spots, all while the taps are off.
4. Test the pressure tank by tapping it. It should sound hollow up the top of the tank and dull, full, at the bottom.

Prefer to leave it to the experts? Our team knows how to diagnose and fix all sorts of water tank pumps in Melbourne. Call 1300 731 578 or get a quote online.

Waterlogged Pressure Tank

A waterlogged pressure tank is one that has lost its compressed air cushion. It causes the pump to rapidly click on and off, known as short-cycling. You can tell if this has happened to your tank a few different ways.

• > The rapid clicking is the first sign that your tank may be waterlogged.
• > Knocking on the side of the tank gives you a dull thud and no hollow sound. This means the tank is completely full of water, with no air bladder.
• > Pushing the pin on the air valve at the top of the tank produces water, not air, shooting out.
• > The pressure gauge needle bounces rapidly when in operation.

A waterlogged tank can occur when the air bladder ruptures. You can’t repair a torn air bladder, and the whole tank will need to be replaced.

In older tanks, the air can slowly escape. This you can repair. Empty the tank completely and inflate the bladder with a bike pump to a couple of PSI below the manufacturer’s recommendation.

Faulty Pressure Switch

A faulty pressure switch can cause a pump to run continuously, or fail to turn on at all. It can also falter into rapid on-off cycling. Look for these signs of a faulty pressure switch:

• > The pump does not shut off and it continues to run. Often you will hear the toilet continuing to run, that soft hissing sound, as this is usually the only place the water can exit.
• > Alternatively, you turn a tap on and no water comes out, meaning the pump fails to start.
• > The pressure surges when the tap is on, sputtering out of a tap as it rapidly cycles on and off.

When you go to inspect the pump for a faulty pressure switch, turn off the power supply. Investigating something electrical, on a water appliance, is dangerous.

Check for blockages as sometimes a ‘no flow’ error, which can trip the system, is caused by a blockage that can be easily removed. Reset the controller and see if that has fixed the problem.

You can check the contact points of the system. Remove the plastic cover to check for dirt or bugs, or for burnt electrical contacts. Bugs and dirt you can clean off, burnt contacts, it will need to be replaced.

You can get an electrician in to test with a multimeter to check the electrical current that is passing through the system. If there is no continuity with closed contacts, the switch is bad and will need to be replaced.

Leaks in the Pipe or System

Leaks in the system are generally loose or corroded thread fittings, perished O-rings or washers, or cracks suction and discharge pipes.

• > Worn down plumber’s tape on fittings, or dried rubber washers at the pump inlet/oulet are common causes of water pump issues. This happens over time and can be easily replaced quite cheaply.
• > Cracks or loose fittings on the intake cause the pump to lose prime and cycle continuously. It loses suction and can’t operate efficiently.
• > You can have vibration stress causing cracks and leaks. A rigid pipe that is connected to a vibrating pipe can fracture over time. This, too, can be easily replaced.
• > The biggest issue is a shaft seal failure in the internal mechanism of the pump. This means the whole pump will need to be replaced.

To check for leaks in the system, turn off the taps and turn off the power to the pump. Dry the area as completely as you can with a towel, and then wait. Where you find the leak can tell you what kind of problem it is.

If the leak is coming from a joint, you can take the hose off, clean off the old sealing tape and wrap fresh tape on the thread. Attach the hose, securing tightly but don’t over-tighten it as this is what strips threads.

Another easy fix is to use flexible hoses, preventing that vibration damage and joint stress.

Failing Pump or Worn Impeller

If water pressure slowly drops and there is a humming noise from the motor, this is usually signs of a worn impeller, the bladed disc inside the pump which creates the flow and pressure of water. Further to this, burning smells or a seized motor means your pump is failing.

If the water pressure is falling, it can mean that sediment in the water is grinding down the blades of the impeller. Those worn blades imbalance the device, and it can knock against the sides of the pipe. Another sign is the motor making all the right noises but no water is moving, which means the impeller is just not pushing water.

If you hear metal on metal grinding noises, or a complete non-operation of the pump, that means the motor or bearings are gone. In both cases you will need to replace the unit. A repair just won’t cut it.

When a Repair Will Fix It

Small problems can often be fixed at home. Clogged filters or inlets can be cleaned out to help with water flow, you can replace worn O-rings and washers and clean out dirt and grime from the pressure switch that isn’t working.

Able to be Repaired	Why
Clogged Filters & Blocked Inlets	Debris or sediment restricting water flow can be cleaned or replaced to restore pressure.
Faulty Pressure Switch	Pitted contacts or a stuck switch can be cleaned or replaced without needing a whole new pump.
Failed Capacitor	If the motor hums but won’t turn, replacing an electrical capacitor often solves the problem.
Leaking Fittings	Deteriorated thread seals or loose brass connections can be re-taped and tightened.

When It’s Time to Replace the Pump

If the problems are more serious, such as a burnt-out motor, cracked pump housing, or if the pump repeatedly fails despite all the repairs you perform, then it is time to replace it.

Need to be Replaced	Why
Burnt-Out Motor Windings	If electrical testing shows internal windings are fried, replacement is required.
Cracked Pump Housing	Physical cracks in the main body or heavy corrosion usually mean the unit is beyond economical repair.
Repeated Failures	If an older pump continually breaks down, replacing it is more cost-effective over time.

Stop the Cycle for Good with PJT Green Plumbing

Short-cycling is your pump telling you something isn’t right, whether that’s a small fix like a dirty pressure switch or a bigger issue like a failing impeller. The good news is that most causes are easy to diagnose once you know what to check, and bringing the experts.

When you’ve got an issue and need water tank repairs in Melbourne, we’ve got the equipment, experience and expertise to get it back on track. Simply contact PJT Green Plumbing and we’ll send a qualified professional to get your system properly diagnosed and sorted.