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Tempering Valve vs TMV: What's the Difference, and Which Does Your Home Need?
Tempering Valve vs TMV: What's the Difference, and Which Does Your Home Need?, a Prime Plumbing & Gasfitting plain-English guide to tempering valve vs tmv for Melbourne homeowners. Below we cover what works, what doesn't, and when to call a licensed plumber.
Quick answer: A tempering valve and a thermostatic mixing valve (TMV) both blend hot and cold water to deliver a safer outlet temperature, but they aren't interchangeable. A tempering valve is a simpler, cheaper device set at around 50 °C, required at the hot water outlet of every Australian home under AS/NZS 3500.4. A TMV is a more accurate, fail-safe device set at 45 °C and required by AS/NZS 3500.4 in healthcare, aged care, early childhood and disability facilities, anywhere users can't reliably regulate their own bathing temperature. The key difference: a TMV will shut off the hot supply if the cold supply fails. A tempering valve won't.
Why hot water needs to be tempered in the first place
Hot water leaving a storage unit or instantaneous gas heater needs to sit at a minimum of 60 °CThat's not negotiable, it's plumbed-in microbiology.
But 60 °C delivered straight to a tap is hot enough to cause a third-degree burn in about five seconds on adult skin, and faster than that on children, elderly people or anyone with reduced sensation in their hands. So the water has to be stored hot and delivered cooler. That's the job of a tempering valve or a TMV.
Australian Standard AS/NZS 3500.4 is the relevant document, it's the part of the National Plumbing Code that covers heated water services. It mandates that water at any sanitary fixture (basin, shower, bath) must not exceed 50 °C in residential settings, and 45 °C in healthcare, aged care, early childhood education and care, schools and disability accommodation.
What is a tempering valve?
A tempering valve is a thermostatic mixing device installed at the outlet of the hot water unit. It blends a measured amount of cold water into the hot supply so the water leaving the unit runs at around 50 °C.
The mechanical heart of a tempering valve is a wax thermostat that expands and contracts with temperature, sliding a piston to open and close the cold-water inlet port. As outlet temperature rises, the wax expands and lets in more cold water. As outlet temperature falls, the wax contracts and lets in less.
It's a robust, simple, cheap device. A residential tempering valve typically costs around $80-$150 for the part, and an installation visit usually runs $250-$450 depending on access and whether existing fittings can be reused.
Where tempering valves are required
Under AS/NZS 3500.4, every new or replacement hot water installation in a residential property in Australia must include a tempering valve at the unit, set to deliver no more than 50 °C at the bathroom fixtures. If your home was built or had its hot water unit replaced any time in the last 20-odd years, you've already got one.
You can usually spot it as a chunky brass or chromed valve on the outlet side of your hot water unit, often with a small adjustment cap on top.
What is a TMV?
A thermostatic mixing valve (TMV) does the same fundamental job, blend hot and cold to a safe temperature, but to a much higher engineering standard. Key differences:
- Tighter temperature accuracy: a TMV holds outlet temperature within ±1-2 °C across normal supply pressure variations. A tempering valve drifts more.
- Fail-safe shutoff: if the cold supply fails (mains break, frozen pipe, isolation valve closed), a TMV will shut off the hot supply within seconds so a user can't be scalded by suddenly-undiluted 60 °C water. A tempering valve doesn't do this.
- Annual servicing requirement: TMVs in commercial settings must be tested and recommissioned every 12 months by a licensed plumber to AS 4032.3, with results logged. Tempering valves don't have this requirement.
- Set point: TMVs are typically set to 45 °C (commercial standard for vulnerable users). Tempering valves are set to 50 °C.
- Cost: A TMV costs more, typically $250-$450 for the valve, plus install. Annual servicing adds another $150-$300 per valve depending on volume.
Where TMVs are required by AS/NZS 3500.4
TMVs are mandatory at sanitary fixtures (basins, showers, baths used by occupants) in:
- Healthcare facilities (hospitals, day surgeries, medical centres)
- Aged care facilities
- Early childhood education and care centres
- Schools (primary and some special-needs settings)
- Disability accommodation (group homes, supported residential services)
The reasoning: in these settings, occupants may not be able to react to sudden water temperature changes, a child, a person with dementia, a person with reduced skin sensation, so the valve has to fail safe.
For commercial TMV servicing in Melbourne, our TMV testing service handles the annual recommissioning and certification.
Tempering valve vs TMV: side-by-side
| Feature | Tempering valve | TMV |
|---|---|---|
| Set-point | ~50 °C | 45 °C (typically) |
| Accuracy | ±2-3 °C | ±1-2 °C |
| Cold-supply failure | Outlet runs hotter | Hot supply shuts off |
| Annual service required | No | Yes (commercial), AS 4032.3 |
| Where required | Residential (AS/NZS 3500.4) | Healthcare, aged care, ECEC, disability, schools |
| Typical part cost | $80-$150 | $250-$450 |
| Typical commissioning service | Replace every 5-10 years on demand | Test and recommission annually |
Service area
Prime Plumbing & Gasfitting services tempering valves and commercial TMV testing across Melbourne's eastern, south-eastern, inner-east and bayside suburbs. See all suburbs we service
Book a tempering valve or TMV service
Call 0475 407 670 or send through the contact form.
- BPC #103414: Building and Plumbing Commission licence
- AS 4032.3: qualified for commercial TMV testing
- 4.8 stars on Google
- Compliance Certificate issued where the work requires one
Can I install a TMV in my home if I want one?
You can. A TMV in a residential home isn't required, but it's not prohibited either. We sometimes install TMVs in homes where:
- A family member has reduced skin sensation (diabetic neuropathy, paraplegia, age-related)
- Young children share a bathroom with adults and the parents want extra peace of mind
- The owner is converting a residence to short-term accommodation and wants commercial-grade safety
- The existing tempering valve has been replaced multiple times and the owner wants a longer-lasting solution
The trade-off is the higher upfront cost and, if you choose to keep it certified annually, the ongoing service cost. Most homes don't need it, but it's a legitimate option.
Common signs your tempering valve or TMV needs servicing
- Outlet temperature has crept up: water at the basin feels hotter than it used to, especially in winter when cold supply is colder
- Outlet temperature has dropped: shower runs lukewarm even with the tap fully hot
- Unstable temperature: water swings between hot and cold during a single shower
- Visible drip at the valve body
- Annual service due (commercial TMVs) or last service was 10+ years ago (residential tempering valve)
A tempering valve failing into a "hotter" mode is the dangerous failure, it's how scald injuries happen. If your basin water feels noticeably hotter than it used to, get the valve checked.
When to call a licensed plumber
This isn't DIY work, tempering valves and TMVs are part of the heated water service and must be installed and certified by a licensed plumber. The Victorian Building Authority maintains a plumbing licence search so you can verify any plumber before booking.
Frequently asked questions
Tempering valves usually have a small adjustment cap, but adjusting them is regulated work, the valve has to deliver no more than 50 °C at the most distant fixture, which means measuring with a calibrated thermometer at flow. Get a licensed plumber to adjust it. A homeowner adjusting their valve up because the shower is "lukewarm" is how children get scalded.
Typically 5-10 years in residential service, depending on water quality. Hard water and high mains pressure shorten the life, sediment builds up around the wax thermostat and the valve drifts. If yours is more than 10 years old and you've noticed unstable temperature, replacement is normally cheaper than trying to service it.
No, only certain commercial and institutional facilities are legally required to have TMVs at sanitary fixtures. Your home needs a tempering valve at the hot water unit, not a TMV at every basin and shower. If your home is part of a registered NDIS supported residence or similar, the TMV requirement may apply, check with the licensing body.
A TMV that fails recommissioning either gets repaired (cartridge or thermostat replacement) or replaced. The certificate is only issued for valves that pass the test, you can't keep using a TMV that's drifted out of spec at a healthcare site. We document the result either way and advise on the cheapest path forward.
Yes, a single TMV can serve a group of fixtures (e.g. all the basins in a ward) provided the pipework is sized correctly and the dead-leg lengths are within AS/NZS 3500.4 limits. Bulk TMVs at a hot water plant supplying a whole wing are common in larger aged-care facilities. Residential is typically one tempering valve at the unit, no per-fixture devices needed.
Sometimes a leaking valve can be re-seated or have its O-rings replaced, but if the valve is more than 5-7 years old, replacement is often cheaper than service. The valve body itself is the part that wears, not just the seals, and a fresh valve gives you another decade of reliable temperature control.
How much does it cost?
Pricing varies with access, existing fittings, and whether the valve is a like-for-like replacement or a new install. Indicative ranges only:
- Residential tempering valve replacement: typically $300-$550 supply and fit
- Residential TMV install: typically $550-$900 supply and fit
- Commercial TMV annual service and recertification: typically $150-$300 per valve, lower per-valve in volume
- Commercial TMV new install: typically $700-$1,200 per valve
We quote in writing first, after looking at the existing installation. Cost depends on the existing pipework, valve location, and how easy it is to isolate during the swap.
- When did the issue start?
- Is it isolated to one fixture or multiple areas?
- Are there any visible leaks, smells or unusual sounds?
- Have you turned off the relevant isolation valve?
- TMV testing Melbourne: annual commercial TMV recommissioning to AS 4032.3
- Hot water systems Melbourne: new and replacement HWS installs including tempering valves
- Hot water replacement Melbourne: like-for-like and upgrade replacements with new tempering valve
