TMV vs Backflow Testing — When Do You Need Each, and Can One Plumber Do Both?

TMV vs Backflow Testing — When Do You Need Each, and Can One Plumber Do Both? — a Prime Plumbing & Gasfitting plain-English guide to tmv vs backflow testing for Melbourne facility managers. Below we cover what works, what doesn't, and when to call a licensed plumber.

Quick answer: TMV testing checks that hot water leaving a tap stays at a safe temperature for vulnerable users (children, elderly, hospital patients) — annual, under AS/NZS 4032.3. Backflow testing checks that contaminated water can't be siphoned back into the public water main — annual, under AS 2845.3. They're entirely different devices testing different risks, with different reporting requirements. But the same Victorian plumber, holding both the TMV testing endorsement and the Backflow Prevention Endorsement, can carry out both tests on the same site visit and produce both annual reports together. Most Melbourne facilities that need one also need the other.

TMV testing — hot water temperature safety

A thermostatic mixing valve sits on the hot supply line just upstream of an outlet (basin, shower, bath). It blends hot water from the storage system (which may be 60-70°C to prevent Legionella) with cold water to produce a controlled mixed-water temperature at the outlet — usually 38°C for healthcare and aged care, sometimes 43.5°C in less-vulnerable commercial settings.

The risk it manages: scalding. An elderly resident or young child can sustain a serious burn from water above 50°C in just a few seconds.

What the annual test checks:

• Outlet mixed-water temperature is still in tolerance
• If the cold supply fails, the valve cuts hot within 5 seconds (failsafe)
• If the hot supply fails, the valve cuts hot cleanly
• No cross-flow between hot and cold supplies

Backflow testing — water contamination prevention

A backflow prevention device sits on the incoming water main (or on a specific high-risk branch). Different designs for different risk levels:

• RPZD (Reduced Pressure Zone Device) — high-hazard premises (medical, dental, factories with chemical processes, food retail with grease-trap, irrigation with chemical injection)
• DCV (Double Check Valve) — medium-hazard premises (many commercial properties, some apartment buildings)
• Single check / dual check — low-hazard residential and small commercial

The risk it manages: during a pressure drop on the public water main (a burst main, a fire-hydrant draw, peak demand) water can flow backwards from a property into the public supply, carrying whatever contamination existed in the property's plumbing. The backflow device mechanically blocks that reverse flow.

What the annual test checks:

• The device's check valves still seat fully under reverse pressure
• The pressure-relief vent (on RPZD) still activates within its rated range
• Test cocks operate cleanly
• No internal corrosion or particle damage to the valve assembly

Yes — if they hold both endorsements. In Victoria, the relevant endorsements are issued by the Building and Plumbing Commission (BPC):

• TMV testing endorsement — covers the AS/NZS 4032.3 test
• Backflow Prevention Endorsement — covers the AS 2845.3 test (separate from the BPC general plumbing licence)

Not every Melbourne plumber holds both. Some specialise. When you're booking, ask for the endorsement numbers and confirm both are current — many facility-management contracts now require it explicitly on the contract.

Prime Plumbing & Gasfitting holds both. BPC #103414 covers the general plumbing licence; the Backflow Prevention Endorsement and TMV testing endorsement are both attached.

If your premises has both TMVs and backflow devices (most aged care, healthcare, childcare and body corporate properties do), running them as one combined annual visit has practical advantages:

1. One visit, less property downtime. A single morning, all amenities back online by lunchtime, instead of two separate visit days.
2. One quote. Fixed-price annual contracts that bundle TMV + backflow are usually 10-20% cheaper than booking them separately.
3. One Compliance Certificate file. Both reports lodged at the same time, with the same site asset register update.
4. One contractor for follow-up. If something fails at audit nine months later, the same plumber who tested it knows the site and the history.
5. Combined visit slots match natural compliance windows. Most facilities prefer their annual compliance work clustered into one month each year, not spread across the calendar.

Combined TMV + backflow annual contracts in Melbourne typically run:

• Single-RPZD + 2-4 TMV site (small medical practice, small childcare): $350-$550 total
• Single-RPZD + 8-15 TMV site (small aged care, body corporate): $650-$1,200 total
• Multi-RPZD + 20+ TMV site (large aged care, hospital, multi-building): quote-by-site

These ranges are a guide only — the actual quote depends on access, device type/age, and how clustered the tests are.

Call 0475 407 670 or send your property address through the form below. We'll quote a fixed-price annual contract covering both — one visit, two reports, one folder of paperwork.

Book combined annual testing →