There is a difference between a hot water system that is failing and one that is simply smaller than the household using it. They feel identical at seven in the morning and they have completely different answers, so it is worth telling them apart before anyone quotes you for a replacement.
The quick version: a failing unit gets worse over time and usually shows other symptoms. An undersized one is perfectly consistent and only ever runs out in the same predictable way.
If you run out at the same point every time, in the same order, and the water that does come through is properly hot, the system is probably working correctly and is simply too small for the demand. If the water is lukewarm, the temperature wanders, or it has been getting gradually worse, that is a fault and it needs looking at.
- Note whether it is consistent or getting worse
- Note whether the hot water is properly hot while it lasts
- Count what actually draws hot water in the morning
- Check the age of the unit
- Get it assessed before agreeing to a replacement
On this page
1. Telling undersized from failing
This is the whole diagnosis, and you can do most of it yourself before anybody arrives.
- Undersized is consistent. It runs out after roughly the same amount of use, every time, and the water is properly hot right up until it is not.
- Failing is progressive. It used to manage the morning and now it does not, and the trend has been downward over weeks or months.
- Lukewarm is a fault. Water that is warm rather than hot points at a thermostat, an element or a valve, not at capacity.
- Wandering temperature is a fault. Hot, then cool, then hot again in one shower is not a size problem.
How long until there is hot water again? A storage unit that reheats in a reasonable time and simply runs out sooner than you would like is behaving normally. One that takes far longer than it used to is not.
2. Sized for the household the house was built for
Most of the detached housing here dates from the 1950s onward, and hot water systems get sized for the household in front of the person installing them. A unit chosen for a family of three in a one-bathroom house is a perfectly good unit. It is just an answer to a question nobody is asking any more.
What has changed is not subtle. Second bathrooms, ensuites, dishwashers, washing machines running most days, and in a lot of houses more people than the original plan assumed. Add a second dwelling on the block and the original sizing is no longer in the same conversation.
So a system can be in good condition, correctly installed and genuinely too small at the same time, and nobody has done anything wrong.
3. Do the morning arithmetic once
It is worth actually counting rather than estimating, because most households underestimate this considerably.
- Count the showers taken between waking and leaving, and roughly how long each runs.
- Add anything else drawing hot water in that window: a dishwasher on a hot cycle, a washing machine, a bath.
- Note whether they overlap or run one after another.
- Compare that against the size of the unit you have.
Overlap matters more than total volume. Two showers running at once draws from the same storage at twice the rate, which is why the same household can be fine on a weekday and short on a Sunday.
4. When it is genuinely a fault
Some symptoms are not about size at all and should be looked at rather than lived with.
- Water at the base of the unit. A leaking tank is not repairable in any meaningful sense and it does not improve.
- Discoloured or rusty hot water. Frequently the sacrificial anode has been spent for some time and the tank has begun paying for it.
- Noise. Banging or rumbling from a storage unit usually means sediment.
- No hot water at all. An element, a thermostat, a pilot or the supply, depending on the type of system.
- Relief valve discharging constantly. Some discharge is normal, a steady stream is not.
Sydney's water is soft, so the usual culprit in a storage unit here is a spent anode or a failed element rather than the scale build-up people expect from harder water elsewhere.
Not sure which it is?
We will tell you whether it is a fault or a sizing problem before quoting you for anything.
5. Repair or replace, and how age decides it
Age is the first thing worth establishing, and it is usually on a plate on the unit. A relatively young system with a failed component is normally worth repairing. A unit well into its life with a leaking tank is not, whatever anyone tries to do for it.
We will not put a number on the life of a system we have not seen, because it depends on the type, the installation and how it has been treated. What we will do is tell you which side of that line yours is on before quoting, rather than declaring it dead on arrival.
If the honest answer is that the system is fine and too small, then replacement is still a legitimate choice. It is just a choice about capacity rather than a repair, and you should be told which one you are buying.
6. What helps before you replace anything
- Stagger the showers. Unglamorous and genuinely effective when the problem is overlap rather than total volume.
- Run the dishwasher and washing machine outside the morning window. Both draw from the same storage.
- Check the thermostat setting is correct rather than low. Worth having looked at, and not something to experiment with yourself given the scalding risk.
- Fix dripping hot taps. A slow drip on the hot side is heated water going down the drain continuously.
- Have the anode checked. On a storage unit it is the part that protects the tank, and replacing one is far cheaper than replacing what it was protecting.
If none of that closes the gap, then the system genuinely is too small, and at least you will be buying the right thing for the right reason.
- Consistent running out is usually capacity. Getting worse over time is usually a fault.
- Lukewarm or wandering temperature is a fault, not a size problem.
- Most houses here were drawn for a smaller household than the one now using them.
- Overlapping use matters more than total volume, which is why weekends are worse.
- Sydney water is soft, so it is normally a spent anode or element rather than scale.
Running out of hot water FAQs
Why do we run out of hot water every morning?
Most often because more hot water is being drawn in that window than the unit stores, particularly where showers overlap. If the water is properly hot until it runs out, and it happens at the same point every day, that is a capacity pattern rather than a fault.
Is lukewarm water a sizing problem?
No. Water that is warm rather than hot points at a thermostat, an element or a mixing valve. A unit that is merely too small delivers properly hot water right up until it runs out.
How do I find out how old my system is?
There is usually a compliance plate on the unit with a date on it. If you cannot find one or cannot read it, we can normally date it from the model. Age is the first thing that decides repair against replace.
Should I just get a bigger unit?
Possibly, but not before somebody has confirmed the current one is working correctly. Replacing a healthy system because of a fault you have not diagnosed is an expensive way to not fix it.
What is an anode and why does it matter?
It is a sacrificial rod inside a storage tank that corrodes so the tank does not. Once it is spent, the tank starts corroding instead. Replacing an anode is considerably cheaper than replacing a tank, and it is the sort of thing worth checking rather than waiting on.
Does hard water cause problems here?
Not really. Sydney's water is soft, so the scale build-up people expect from harder-water areas is not the usual story. In a storage unit here the common failures are a spent anode or a failed element.