At an older apartment building on First Avenue in Dandenong VIC 3175, our team at Your Choice Plumbers was called out after the occupants were left with no hot water at all.
At first glance, “no hot water” sounds like a common plumbing call. But this job quickly proved to be very different. The issue was not with a standard mains pressure system. Instead, the building was still operating on an original gravity-fed electric hot water system located in the roof space, which meant the diagnosis and repair process required a very different approach.
This is exactly the type of situation where homeowners or residents start asking, “why is there no hot water when the system still has power?” or “can an older gravity-fed hot water system stop flowing because of an airlock?” As an experienced plumber Dandenong, we know that rare older plumbing systems need proper investigation rather than standard assumptions.
The Problem – No Hot Water from a Gravity-Fed System
When we arrived, the key symptom was clear: no hot water was coming from the taps.
On a typical modern system, that would often point toward an issue with heating, power supply, tempering, or water delivery pressure. But with an older gravity-fed setup, the plumbing behaves very differently because these systems rely on:
- a roof-mounted storage arrangement
- a balancing tank
- a float switch to refill the tank
- and gravity, rather than mains pressure, to move hot water through the pipework
That meant the job had to be approached with an understanding of how these older systems actually operate.
Accessing the Roof Space and Finding the First Fault
The first step was to access the roof space and inspect the gravity-fed system directly.
Once inside, we found that the balancing tank was completely empty.
That was the first major clue and it immediately narrowed the diagnosis. If the balancing tank is empty, the system cannot refill properly, which means hot water delivery to the taps becomes impossible regardless of whether the heating side is still functioning.
This pointed directly to a float switch failure.
In a gravity-fed system like this, the float switch is responsible for allowing the balancing tank to refill as water is used. Once it fails, the system stops replenishing itself correctly and hot water flow eventually stops altogether.
Replacing the Failed Float Switch
After identifying the failed component, we sourced a suitable replacement float switch from Reece Plumbing Dandenong and installed it into the system.
Once the new float switch was fitted, the balancing tank began refilling again as it should.
At that stage, part of the problem was solved. The system had regained its ability to replenish water, which was a necessary first step. But the job was not finished yet, because even after the tank began filling normally again, hot water still was not flowing to the taps.
That confirmed there had to be a second fault.
The Secondary Problem – A Hidden Airlock in the Hot Water Pipework
Because gravity-fed systems operate with much weaker delivery pressure than modern mains pressure setups, they are far more vulnerable to airlocks.
In simple terms, an airlock forms when trapped air inside the pipework interrupts the flow path so badly that the water can no longer move properly through the line.
That was exactly what had happened here.
Once the float switch issue was resolved, the system was technically capable of operating again, but the hot water line was still blocked hydraulically by trapped air.
This is why rare older systems need careful step-by-step diagnosis. If the repair had stopped after replacing the float switch, the occupants still would not have had usable hot water.
Using a Specialist Method to Clear the Airlock
To clear the airlock, we used a specialised bridging method through the washing machine tap connections.
The process involved:
- connecting the hot and cold outlets together temporarily
- allowing strong mains cold water pressure to enter the hot water pipework
- using that pressure to dislodge the trapped air pocket inside the gravity-fed line
This is not a standard step on a normal mains pressure hot water system. But on gravity-fed systems, it can be the correct technique because the gravity side simply does not have enough force on its own to push the trapped air through.
After only five to ten minutes, the trapped air was forced clear and hot water began flowing steadily from the system again.
Why This Was a Two-Fault Hot Water Problem
What made this job particularly important was that the system had two separate faults at the same time:
- a failed float switch preventing the balancing tank from refilling
- an airlock in the hot water pipework stopping delivery even after refill was restored
That is why the problem could easily have confused someone unfamiliar with older gravity-fed systems.
One fault explained why the system had run empty. The second fault explained why hot water still would not flow even after the first repair was completed.
This is exactly why proper hot water system diagnosis matters so much — because the first visible repair is not always the full answer.
The Result – Hot Water Restored Without Replacing the Entire System
Once both faults had been addressed, the building had:
- the failed float switch replaced
- the balancing tank refilling properly again
- the hot water pipework cleared of the airlock
- normal hot water flow restored to the taps
That was a strong outcome, especially on a rare and older plumbing system that many plumbers may not have approached with confidence.
Instead of rushing toward unnecessary full replacement, the job was solved through careful diagnosis and an understanding of how this specific style of system actually worked.
Why This Job Matters
This case is a strong example of why older or unusual plumbing systems need specialist thinking.
A gravity-fed hot water system does not behave like a standard modern mains pressure system, so diagnosing it properly means understanding:
- how the balancing tank operates
- what role the float switch plays
- how airlocks affect weak-pressure pipework
- and how to clear those airlocks safely and effectively
Without that understanding, this could easily have turned into:
- a misdiagnosed appliance failure
- an incomplete repair
- or unnecessary replacement advice
Instead, the homeowner received a solution based on actual system behaviour and real fault finding.
Our Home Plumbing Experts Approach
At Your Choice Plumbers, we do not just work on common plumbing problems. We also take the time to understand and solve older, less common, and more technical systems properly.
That means when a plumbing issue is unusual, we do not default to guesswork. We test it, isolate it, and work through it until the real cause is clear.
That is the difference between simply recognising a symptom and actually solving the plumbing problem behind it.
Need a Plumber in Dandenong?
If you are dealing with no hot water, an older storage system, or a plumbing setup that other contractors have struggled to diagnose properly, visit our Plumber Dandenong page to learn more about how we help local homeowners and apartment properties.
You can also learn more about our hot water system repairs service and broader home plumbing services across Melbourne.
