TMV testing is the check that a thermostatic mixing valve (TMV) still delivers water warm enough to wash with, not hot enough to scald. The valve sits between the hot water unit and the tap and blends stored hot water with cold. In NSW, TMV testing is a compliance job on healthcare, aged care, childcare, school and disability bathrooms: the valve has to be commissioned, tested and written up. Here is what it does, where it is required, and what a test involves.
TL;DR
A TMV blends stored hot water down to a safe tap temperature. NSW hospitals may only use an approved warm water system, usually a TMV, on patient ablution outlets. Aged care, patient care areas, childcare, schools and disability facilities have a 45°C limit at personal-hygiene fixtures, met with a TMV or a thermostatically controlled tap. Field-testing follows AS 4032.3 and the manufacturer’s instructions; check the interval for your facility type. Hospital sites also run a monthly temperature check. The owner should receive a written report.
What does a TMV do, and why is the tank hotter than the tap?
Hot water is stored hotter than anyone should put their hands in. For Legionella control, NSW Health’s hospital water policy treats a hot water system as one designed to heat and deliver water at a temperature of at least 60°C. At that temperature the water will scald, so a TMV mixes in cold and holds a set warm temperature at the tap. The same policy describes the device as mixing cold and hot water to produce warm water for personal ablutions that will not scald people.
In hospitals, personal-hygiene outlets in patient areas are set in a warm range: 38.0°C to 40.5°C for children, 40.5°C to 45.0°C for adults, with a thermal shut-off if the cold supply fails. The tank stays hot enough to control bacteria. The tap stays warm enough to use.
Where are TMVs required in NSW?
Hospitals, including public and private hospitals and nursing homes as defined in that NSW Health policy, must not install a warm water system unless it is of a kind approved in writing. Approved systems include TMVs. All bathing and ablution locations that patients can normally reach must have an approved warm water system.
Outside hospitals, Building Commission NSW’s advisory note on heated water temperatures sets out the rule. It was issued in July 2026 and supersedes the earlier note on temperature control devices. Heated water for personal hygiene must be delivered at no more than 45°C in the residential part of an aged care building, a patient care area in a health-care building, the part of an early childhood centre or primary or secondary school used by children, and any facility designated for use by people with a disability. Everywhere else the limit is 50°C.
At the 45°C sites the device must be a thermostatic mixing valve or a thermostatically controlled tap. At 50°C sites it can also be a tempering valve or a water heater limited to 50°C. A device is required on a new heated water service and whenever a water heater is replaced. It is not required when only a valve, element or thermostat is replaced, or a single tap.
A TMV is a different device from a backflow preventer. Backflow protects the drinking supply; a TMV protects the person at the tap. See backflow testing explained if you have both on the same site.
How often are TMVs tested and serviced?
The interval depends on the facility. Field-testing, maintenance and replacement of TMVs are set out in AS 4032.3. Follow that standard, the manufacturer’s service instructions, and the requirement for your facility type rather than assuming one calendar for every site.
Hospital warm water systems have an extra, prescribed check under the same NSW Health policy: a monthly temperature safety check from at least one ablution outlet (preferably a hand basin) on each TMV, with the temperature recorded. If the reading varies by 2°C or more from the specified operating range after a 20-second stabilisation, the system is isolated until it is checked, adjusted or repaired.
Which facilities need what, and how often is it checked?
NSW Health and Building Commission NSW set different requirements depending on the facility:
| Facility or building type | Device required | Outlet temperature limit | How often it’s tested |
|---|---|---|---|
| Hospitals – patient ablution outlets | Approved warm water system (usually a TMV) | 38.0–40.5°C for children; 40.5–45.0°C for adults | Monthly temperature check on each TMV, plus AS 4032.3 field-testing |
| Aged care (residential part), patient care areas, early childhood centres and schools (parts used by children), disability facilities | TMV or thermostatically controlled tap | Not more than 45°C | Set out in AS 4032.3 and the manufacturer’s instructions |
| All other buildings: new heated water services and heater replacements | TMV, thermostatically controlled tap, tempering valve or a water heater limited to 50°C | Not more than 50°C | Set out in AS 4032.3 and the manufacturer’s instructions |
Check AS 4032.3 and your valve’s manufacturer instructions for the exact interval on your device.
What does a TMV test involve?
The NSW Health commissioning and maintenance report records whether the valve was commissioned or serviced, whether components were inspected and cleaned, whether non-return valves were checked, whether the mixed temperature was set, and whether a thermal shutdown test passed. It also lists the outlets the valve serves, the temperature range used, any parts replaced, and the date the next service is due.
If the valve will not hold temperature or will not shut down, it is repaired or replaced and then retested. That is licensed plumbing work, not a DIY adjustment.
Who may do the work, and what does the owner receive?
In NSW, TMV commissioning and servicing is licensed plumbing work. For hospital warm water systems, NSW Health also requires the person doing it to be a plumber licensed by NSW Fair Trading, trained by a registered training organisation, and experienced in TMV maintenance. Staff without those qualifications may only help under the direct supervision of that plumber.
After a hospital commissioning or service, the licensee submits the report within two working days. Under the NSW Health policy, the original goes to the owner or occupier and is kept on site for at least seven years, with a copy available for inspection. On other sites you should still receive a written commissioning or maintenance report covering the tests done. Unlike a backflow device, a TMV result is not lodged with the water authority.
Donza Plumbing installs, services and tests TMVs: see TMV testing and servicing. The work sits alongside backflow prevention and testing, including on commercial and specialist sites. If a valve is due, or you are not sure whether the bathroom needs one, request a callback.