Answer one question first.
Did it drop off suddenly, over a day or two, or fade gradually over a year or more? A sudden drop points to a failed part. A slow fade points to sediment, or to more people using the same tank.
Call R&G on 0461 330 531. $0 call-out fee.
If your hot water runs out faster than it used to, the useful question is not how long it lasts. It is whether the change was sudden or gradual.
Those two patterns have completely different causes, and one of them is a cheap repair rather than a new system.
Sudden Drop or Slow Fade
Nothing else narrows it as fast as this.
| What happened | Where to look |
|---|---|
| Fine last week, a fraction of it now | A failed element or thermostat. Repairable |
| Slowly worse over a year or more | Sediment reducing the usable volume, or the household has grown |
| Only when two outlets run together | Capacity or flow rate, not a fault |
| Fine in the morning, gone by evening | A controlled load tariff heating overnight only, and demand outrunning it |
| Goes lukewarm rather than cold | A different fault entirely, usually the tempering valve |
The useful way to tell us is the “but”. It still gets properly hot, but it only lasts a few minutes. Or there is plenty for one shower but nothing for the second. Those sentences separate a broken part from a tank that is simply too small for the house.
If you have no hot water at all rather than not enough, that is a different problem with a different answer.
The One-Third Clue on an Electric Tank
This is the fault most worth knowing about, because it looks like a dying hot water system and it is usually a part.
If your unit has two heating elements, and many do, one sits high in the tank, and one sits low. The lower element does most of the work, heating the bulk of the water. The upper one heats the top portion.
When the lower element or its thermostat fails, the upper one keeps going. So you still get genuinely hot water; you just get a fraction of the tank instead of all of it, and it runs out startlingly fast.
The giveaway is that it happened suddenly. One week you had normal hot water; the next you had a few minutes of it. Sediment and a growing family do not work like that.
It is a repair, not a replacement, and on an otherwise sound tank it is the right answer. Which is worth knowing before anyone quotes you for a new system off the back of “it runs out quickly”.
If your unit has a single element, this fault cannot be the cause, and the diagnosis moves to the thermostat or to capacity.
Sediment, and Why an Old Tank Holds Less Than It Says
Two things are true about every storage tank, and together they explain the slow fade.
First, a tank never delivers its rated volume as usable hot water. Cold water enters at the bottom as hot leaves the top, and the two mix as the level draws down, so the last part of the tank arrives warm rather than hot. The number on the label is the volume it holds, not the volume of showers in it.
Second, minerals settle out of the water and build up in the base over the years. That layer takes up space the water used to occupy,y and it sits between the lower element and the water it is meant to heat. Both effects pull in the same direction, which is less hot water than you used to get from the same unit.
A tank that has never been serviced has had years to accumulate it. Draining and flushing is part of what a water heater service is for, and it is the one piece of hot water maintenance that actually recovers lost performance rather than just preventing failure.
Worth being straight about the limit, though. On a very old tank with heavy build-up, flushing helps, but it does not turn it back into a new unit.
If Yours Is a Continuous Flow Unit
A flat box on an exterior wall rather than a cylinder. It has no tank, so it cannot run out, and if yours seems to, then something else is happening.
What people usually mean is that it goes cold when a second tap opens. A continuous flow unit heats water as it passes through, and it can only heat so much per minute. Two showers, or a shower and a kitchen tap, can exceed its rate, and the water arriving at both drops in temperature.
That is a sizing issue rather than a fault. The unit is doing what it was specified to do, and the household is asking for more than that.
The other version is the opposite problem. These units need a minimum flow to fire at all, so a tap opened only slightly, or a property with marginal pressure, can leave you with cold water from a unit that is working perfectly. The fix there is the flow it needs, not the unit.
What Is Worth Fixing, and What Is Not
Elements, thermostats, and tempering valves are repairs, and on a tank that is otherwise sound, they are the right call every time.
Flushing out sediment is worth doing, and it is worth having realistic expectations of an old unit.
Where it stops being worth it is a tank old enough that nobody remembers it going in, one that is leaking, or a unit that is genuinely undersized for the household it now serves. Repairing capacity you never had is not a repair, and a third call-out in two years costs more than doing it once.
What a repair costs depends entirely on which part failed, so we will not pretend there is one number. The guide to hot water system repair costs in Sydney breaks it down by fault, and the hot water systems page covers replacement and sizing if that is where you have landed.
One thing not to do in the meantime is wind the thermostat up to buy more hot water. You will store water hotter than anyone should have on their skin, you will not fix a failed element, and if the tempering valve is also tired, the risk ends up at the kitchen tap.
Three answers and we can usually tell you on the phone
Whether the change was sudden or gradual, what type of unit you have, and the capacity printed on its label. Those three separate a failed element from a tank that was never big enough. Call R&G on 0461 330 531. $0 call-out fee.
Frequently Asked Questions
Why does my hot water run out after five minutes when it used to last much longer?
A sudden drop like that usually means a failed heating element or thermostat rather than a dying tank. On a unit with two elements, the lower one does most of the heating, so if it fails, the upper one still gives you genuinely hot water from the top portion of the tank only. It is a repair and worth establishing before anyone quotes a replacement.
Does sediment in a hot water tank reduce how much hot water I get?
Yes, in two ways. The build-up takes up space water used to occupy, and it sits between the lower element and the water it is meant to heat. That is why the decline is gradual over years rather than sudden. Draining and flushing recovers some of it, though on a very old tank with heavy build-up it helps rather than transforms.
Is my hot water tank just too small?
It is if the hot water has always run out rather than recently started to, or if the household has grown since the unit went in. Read the capacity off the label on the unit and bear in mind a tank never delivers its rated volume as usable hot water, because cold entering the bottom mixes as the level drops. A sudden change is a fault; a long-standing shortfall is sizing.
Why does my continuous flow hot water go cold when someone else turns on a tap?
Because it heats water as it flows through and can only heat so much per minute. Two outlets running together can exceed that rate, so the temperature at both drops. Nothing has failed. It is a sizing question, and the answer is either staggering use or a unit rated for the household’s actual demand.
Can I just turn the thermostat up to get more hot water?
We would not. It stores water hotter than anyone should have on their skin, it does not fix a failed element, and if the tempering valve that blends the bathroom supply is also worn, the extra heat ends up available at the kitchen tap, which is usually not blended. Fix the cause instead.
Repair it if it can be repaired.
We test and replace elements, thermostats and tempering valves, flush storage tanks, and size and install replacements where a repair is not the answer, across the Upper North Shore, the Hills District and the Parramatta and Ryde corridor. Fixed price before anything starts, no call-out fee. See hot water system, or emergency plumbing if the unit is leaking.
