Running out of hot water is one of the most common plumbing complaints in Melbourne homes, and it’s rarely just bad luck. There’s usually a specific, fixable reason behind it.
Your System Is Undersized for Your Household
This is the single biggest cause, and it’s more common than people think, especially in homes where the family has grown since the system was installed. Sustainability Victoria notes that storage systems are sized to household size, while continuous flow systems are sized to the number of hot water outlets running at once, not the number of people. A system that was fine for two people can fall short once teenagers move in or a third bathroom gets added.
The general rule of thumb is around 50 litres of hot water per person per day. If your household has grown but your tank hasn't, running out isn’t a fault, it’s simply a sizing problem.
Sediment Build-Up in the Tank
Over time, minerals in the water settle at the bottom of a storage tank, forming a layer of sediment. This does two things: it reduces the effective water capacity of the tank, and in electric systems, it can insulate the heating element from the water above it, making the system work harder and heat less effectively. If your hot water system is more than a few years old and you’ve noticed it running out faster than it used to, sediment build-up is a common and often overlooked cause.
A Faulty Thermostat or Heating Element
In electric hot water systems, a failing thermostat can stop the element heating water to the correct temperature, or stop it heating at all. You might still get some hot water, just not as much or as hot as usual. This tends to get worse gradually rather than failing all at once, which is why it’s easy to miss until it becomes a daily annoyance.
Running out of hot water every morning? Call Ezy-Plumb and we’ll find out why.
Gas Supply or Pilot Light Issues
For gas hot water systems, an inconsistent pilot light, a faulty gas valve or a build-up of dust and debris around the burner can all reduce how effectively the unit heats water. Gas storage systems that seem to run out faster than usual, or take longer to reheat between uses, are often signalling one of these issues rather than a sizing problem.
An Undersized or Overloaded Continuous Flow System
With instantaneous gas hot water systems, there’s no tank to run out, but there is a flow rate limit. Run the shower, dishwasher and washing machine at once and you can easily exceed what the unit was designed to heat simultaneously, leaving whichever tap was turned on last with lukewarm water. This isn’t a fault, it’s the system doing exactly what it’s rated for, just being asked to do more than it can handle at once.
A Tempering Valve That’s Drifted Out of Adjustment
Every hot water system in Victoria needs a tempering valve to blend scalding-hot stored water down to a safe delivery temperature. According to the Victorian Building Authority, these valves need roughly a 10°C difference between storage and delivery temperature to work correctly. If a tempering valve drifts or fails, it can end up mixing in more cold water than it should, making your hot water feel like it’s running out faster even though the tank itself is fine. We’ve covered exactly how this system works in our article on the 50°C hot water rule in Australia.
The System Is Simply Reaching the End of Its Life
Most storage hot water systems last somewhere between 8 and 12 years. As they age, efficiency drops, sediment builds faster, and components like elements and thermostats become more prone to failure. If your system is in this age range and problems are becoming more frequent rather than a one-off, it may be more cost-effective to replace it than keep repairing it.
Practical Tips Before You Call a Plumber
- Check whether the problem started around the same time your household size or routine changed
- Note whether it’s happening with every use or only when multiple taps run at once
- Check the age of your system; anything past 8 to 10 years is worth a professional look/li>
- For gas systems, check the pilot light is burning steadily and blue, not yellow or flickering
- Avoid adjusting a tempering valve yourself; incorrect adjustment is a genuine scalding risk
Common Mistakes to Avoid
The most common mistake is assuming an aging system just needs replacing without checking for a simpler cause first.
The opposite mistake also happens: repeatedly patching an old system that’s genuinely reached the end of its service life, when a new, correctly sized unit would be more reliable and often cheaper to run. If you’re due for a replacement, it’s worth confirming the appliance chosen is actually sized for your household, not just a like-for-like swap of whatever was there before.
Not sure if it’s worth repairing or replacing? Call Ezy-Plumb for an honest opinion.
When to Call a Professional
If hot water is running out faster than it used to, taking longer to reheat, or a gas unit’s pilot light won’t stay lit, it’s time to bring in a licensed plumber. Hot water is also classified as an essential service under Victorian tenancy law, so if you’re renting, a failure needs to be treated as an urgent repair rather than something that can wait weeks to be actioned.
Final Thoughts
Running out of hot water usually comes down to one of a handful of causes: a system that’s too small for your household, sediment build-up, a failing component, or simply old age. Working out which one it is early saves you cold showers and, in most cases, a fair bit of money.
If you have a plumbing emergency right now, call Ezy-Plumb and get it sorted fast. Our team also handles emergency plumbing across Melbourne’s Bayside suburbs.
FAQs
Q: Why does my hot water run out so quickly?
Ans: The most common reasons are an undersized system for your household, sediment build-up in the tank, or a faulty thermostat or heating element.
Q: How much hot water does the average household use per day?
Ans: Around 50 litres per person per day, according to Sustainability Victoria, though actual use varies with shower length and habits.
Q: How long do hot water systems usually last?
Ans: Most storage systems last around 8 to 12 years, depending on the type, water quality and how well they’ve been maintained.
Q: Is running out of hot water considered an emergency repair in a rental?
Ans: Yes. A failure of hot water supply is classified as an urgent repair under Victorian tenancy law, and landlords must act without delay.
Q: Should I repair or replace an old hot water system?
Ans: It depends on the age and the fault. Simple issues on younger systems are often worth repairing, while systems near or past 10 years old may be more economical to replace.
Q: Do I need a licensed plumber to service a gas hot water system?
Ans: Yes. Gas hot water servicing in Victoria must be carried out by a licensed gasfitter, and rental properties require a check every two years. See Energy Safe Victoria for the current requirements.
