Hot Water Too Hot? Tempering Valves and the 50°C Rule in Victoria
If the hot tap in your bathroom runs hot enough to be unusable on its own, that is not just uncomfortable. In most Melbourne homes it means something has failed, because the water arriving at a basin, bath or shower is supposed to be limited before it gets there.
The number is 50 degrees, and there is a second number behind it that explains why the limiting is needed at all. This covers both, the small valve that does the work, how to tell whether you have one, and how to tell when it has stopped working.
60°C
Minimum storage temperature, to control Legionella
50°C
Maximum delivered to basins, baths and showers in a home
45°C
Maximum in aged care, healthcare, schools and early childhood
The Rule in One Line
Heated water delivered to outlets used for personal hygiene must not exceed 50 degrees in a home, and must not exceed 45 degrees in aged care, healthcare, early childhood services, schools and accessible facilities. Those limits sit in the National Construction Code.
Personal hygiene outlets means the basin, the bath and the shower. The kitchen sink and the laundry trough are not in that category, which is why your kitchen tap can legitimately run hotter than your bathroom one.
Why There Are Two Numbers
Here is the tension that the whole arrangement exists to resolve.
Hot water has to be stored at a minimum of 60 degrees, because water sitting below that temperature allows Legionella bacteria to grow in the tank. That requirement is in the plumbing standard and it is not negotiable.
But 60 degree water arriving at a child’s bath tap is dangerous. So the system stores hot and delivers cooler, and something in between has to drop the temperature. That something is a tempering valve or a thermostatic mixing valve.
This is why turning your hot water thermostat down to make the taps safer is the wrong fix. It removes the Legionella protection and leaves you with a different problem.
How Hot Is Too Hot?
The gap between those two numbers sounds small. In terms of how fast water injures a child, it is enormous.
Scald timings from Australian child safety guidance. 50 degrees is a low-risk delivery temperature, not a bathing temperature.
At 60 degrees it takes about one second to cause a full thickness burn. At 50 degrees it takes roughly five minutes to cause a severe scald. That difference, one second against five minutes, is the entire reason the limit exists. Five minutes is long enough for a child to react and for an adult to intervene. One second is not.
Worth knowing separately: a safe bath temperature for a child is 37 to 38 degrees, so you still mix cold with hot to get there. A compliant 50 degree tap is not a tap you can fill a baby’s bath from without thinking.
Tempering Valve or TMV?
Two different devices do this job and the difference between them matters more than the names suggest.
The Tempering Valve
The common domestic device, made to AS 4032.2. It blends stored hot water with cold to bring the delivered temperature down, and in a normal house it does that job perfectly well.
Its limitation is what happens when something goes wrong. If the cold supply to the valve fails, a tempering valve has no shut-off. It keeps delivering, potentially at full stored temperature. That is a brief window of 60 degree water at a tap with nothing to stop it.
The Thermostatic Mixing Valve
A TMV, made to AS 4032.1, holds the outlet temperature within about two degrees and does the thing a tempering valve cannot: if the cold supply fails, it shuts off the hot water flow within seconds.
That fail-safe is why TMVs are required where vulnerable people use the water, and why tempering valves are not permitted in those settings. In aged care, healthcare, early childhood services and schools the temperature has to be controlled by a TMV complying with AS 4032.1 or by a thermostatically controlled tap.
Which One Should You Have?
For an ordinary Melbourne house, a tempering valve is the standard and compliant answer. If your household includes young children, someone elderly, or anyone who could not react quickly to a sudden change in water temperature, a TMV is worth asking about even though it is not required in a private home.
If you run a childcare service, a school, a clinic or an aged care facility, the TMV requirement applies to you and so does the testing regime further down.
Do You Already Have One?
Almost certainly, if the hot water system was installed or replaced in recent decades. The valve is a small brass fitting on the pipework at the hot water unit, usually with a cold water line running into it and often with a temperature setting marked on the body.
The quick test is at the tap rather than at the valve. Run the bathroom hot tap on its own for a couple of minutes and put your hand under it. Water limited to 50 degrees is distinctly hot and uncomfortable to hold your hand in, but you can hold it there. Water that you cannot keep your hand under at all, or that makes you pull away immediately, is a sign to get it checked.
Do not use a kitchen tap for this test. The kitchen is not a personal hygiene outlet, so it is not limited, and a hot kitchen tap tells you nothing about the bathroom.
Older homes are where the gap tends to be. A house with original pipework that has never had the hot water system replaced may never have had a tempering valve fitted. If that sounds like your place, our guide on galvanised pipes in older Melbourne homes covers the other things worth checking at the same time.
Signs Yours Has Failed
- The bathroom hot tap is scalding on its own. The clearest sign. A working valve should make it hot but tolerable for a moment.
- The temperature wanders. Hot, then cooler, then hot again with nothing else running in the house points to a valve losing its ability to hold a setting.
- The shower goes cold when a tap opens elsewhere, then overshoots hot when it closes.
- Hot water seems weaker than it used to be. Valves can block internally, which restricts flow as well as affecting temperature.
- It has never been serviced. These are mechanical devices with seals and a thermostatic element, and they do not last indefinitely.
- The hot water system was replaced but the valve was not. A new unit on an old tempering valve is a common and easily missed combination.
A failed valve rarely announces itself with a leak, which is why these go unnoticed for years. The failure mode that matters is silent: the limiting simply stops working and the tap starts delivering stored temperature.
Testing and Servicing
What is required depends on the kind of building, and the difference is substantial.
In a Private Home
There is no mandated annual test on a domestic tempering valve. That does not make it maintenance free. Have the delivery temperature checked whenever a plumber is at the hot water system anyway, and treat a valve that has never been looked at in a decade as due for attention.
If the hot water unit is being replaced, replace the tempering valve with it. The labour is already being paid for and the old valve is the same age as the unit coming out.
In Care, Health and Education Settings
Here the regime is formal. TMV field testing, maintenance and replacement must comply with AS 4032.3, which the National Construction Code requires. In practice that means annual testing, with a major service replacing the thermostat and seals on roughly a five year cycle.
Commissioning should also verify the outlet temperature at both full flow and trickle flow, with the readings recorded. A valve that reads correctly wide open can still deliver badly at a low flow rate, which is exactly the condition a hand basin creates.
If you manage a facility like this, the records are as much the deliverable as the work. Our commercial plumbing page covers how we handle recurring compliance work.
What Not to Do
Three things worth avoiding, because each one makes the situation worse rather than better.
Do not turn the storage thermostat down to cool the taps. Storage has to stay at 60 degrees minimum for Legionella control. Dropping it trades a scald risk for a bacterial one and does not fix the valve that is actually at fault.
Do not adjust the tempering valve yourself. It looks like a simple setting and it is not. Getting it wrong leaves either a scald risk or a valve that cannot deliver usable hot water, and on most units this is licensed work in any case.
Do not treat a scalding tap as a quirk of the house. If it has been like that for years, that is not evidence it is fine. It is evidence that nobody has checked it for years.
Talk to a Licensed Plumber in Melbourne
Checking a delivery temperature and testing a tempering valve is a short visit, and it is the kind of thing worth doing before it matters rather than after. If your bathroom tap runs scalding on its own, or the hot water unit has been replaced and the valve has not, Plumb Construct can check it, service it or replace it. We are licensed and we work across Melbourne.
Related Plumbing Services
Frequently Asked Questions About Tempering Valves
What temperature should hot water be at the tap in Victoria?
No more than 50 degrees at outlets used for personal hygiene, meaning the basin, bath and shower, in a normal home. The limit drops to 45 degrees in aged care, healthcare, early childhood services, schools and accessible facilities. Kitchen sinks and laundry troughs are not personal hygiene outlets, so they are not subject to the same limit and can legitimately run hotter.
Why is hot water stored at 60 degrees if 50 is the limit at the tap?
Because the two numbers solve different problems. Water stored below 60 degrees allows Legionella bacteria to grow in the tank, so the plumbing standard sets 60 degrees as the storage minimum. Water at 60 degrees is unsafe at a tap, so a tempering valve or thermostatic mixing valve blends it down before delivery. That is why turning the thermostat down is not a safe way to cool your taps.
What is the difference between a tempering valve and a thermostatic mixing valve?
A tempering valve, made to AS 4032.2, blends hot and cold to limit the delivered temperature, and it is the standard domestic device. A thermostatic mixing valve, made to AS 4032.1, holds the outlet within about two degrees and shuts off the hot water flow within seconds if the cold supply fails. A tempering valve has no such shut-off and keeps delivering, which is why TMVs are required where vulnerable people use the water.
How do I know if my tempering valve has failed?
Run the bathroom hot tap on its own for a couple of minutes. Water limited to 50 degrees is hot and uncomfortable but you can briefly hold your hand under it. If you cannot, or if the temperature wanders noticeably with nothing else running, the valve needs checking. Other signs include the shower overshooting hot after another tap closes, and reduced hot water flow, since these valves can block internally.
How often does a tempering valve need servicing?
In a private home there is no mandated annual test, though having the delivery temperature checked whenever a plumber is at the hot water system is sensible, and the valve should be replaced along with the unit. In aged care, healthcare, education and similar settings, testing and maintenance must comply with AS 4032.3, which in practice means annual testing with a major service replacing the thermostat and seals around every five years.
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