How to install a tempering valve on a hot water system

🔧 Installing a Tempering Valve on a Hot Water System — Australian Trade Guide

Why is a tempering valve essential for Australian hot water systems?

Tempering valves are installed on hot water systems to blend heated water with cold water and deliver safe outlet temperatures to fixtures, typically to sanitary outlets in residential and many commercial applications. In Australia, installation and setting of tempering valves must comply with the PCA, AS/NZS 3500, and manufacturer instructions to achieve scald protection, maintain system performance, and satisfy commissioning requirements.

Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials.

What skill level is required to install a tempering valve in Australia?

Advanced — Estimated time: 2–4 hours

What specific tools are required for tempering valve installation in Australia?

What materials are needed for a compliant tempering valve installation in Australia?

Safety Requirements

Step-by-Step Guide

Step 1: Assess the system and confirm compliance requirements

1️⃣ Identify the application

Confirm whether the valve is being installed on a new hot water service, as part of a replacement, or to rectify non-compliant delivery temperatures. Determine which fixtures are to receive tempered water and whether the kitchen sink is included under the specific project design and local authority interpretation.

Review the required delivery temperature under AS/NZS 3500.4 and applicable state requirements. In most residential applications, heated water delivered to sanitary fixtures used primarily for personal hygiene must be limited to 50°C, and to 45°C in certain aged care, childcare, disability care or healthcare environments where applicable.

💡 Always confirm whether the installation requires a standard tempering valve or a higher-specification TMV with testable performance.

Step 2: Verify hot water unit suitability and valve sizing

2️⃣ Check system operating conditions

Confirm:

Select a tempering valve with the correct nominal size, usually 15 mm or 20 mm, based on calculated flow demand and fixture load. Check manufacturer data for minimum flow, pressure differential, and maximum inlet temperatures.

Where storage temperature is maintained at 60°C or above for legionella control, ensure downstream tempering arrangement provides compliant delivery temperature without compromising system hygiene strategy.

Step 3: Plan the pipe layout

3️⃣ Set out the installation

Locate the tempering valve as close as practical to the hot water unit outlet while allowing access for adjustment, service, strainers and future replacement. Follow the directional markings for:

Plan for:

Maintain a neat, serviceable arrangement with sufficient clearance for removal of caps and servicing components.

Step 4: Isolate, drain and prepare the pipework

4️⃣ Make the system safe to work on

Shut off the cold water supply to the hot water service and isolate any relevant branch lines. Open a downstream hot tap to relieve pressure and drain enough water to work on the selected section of pipe.

If working on an electric storage unit, isolate power at the switchboard. If working near gas appliances, ensure appliance isolation procedures are followed by a licensed gas fitter where required.

Mark cut points carefully and allow for valve body length, unions and any additional isolation valves or fittings.

Step 5: Cut in isolation valves and connection points

5️⃣ Prepare serviceable valve connections

Cut, deburr and clean the pipework. Install full-flow isolation valves on the:

Where the manufacturer requires integral or separate strainers and non-return valves, install them in the correct orientation. Many failures in tempering valve performance are caused by debris or incorrect check valve placement.

Use compatible joining methods:

Support all pipework to prevent loading on the valve body.

Step 6: Install the tempering valve

6️⃣ Fit the valve in the correct orientation

Install the tempering valve observing the embossed flow direction and identified ports. Typical arrangement:

Ensure unions are aligned and not under tension. Tighten to manufacturer torque guidance where available. Do not overtighten threaded brass bodies or tails.

If the valve is wall-mounted or bracket-supported, secure it so that future servicing does not disturb adjoining pipework.

💡 A well-supported valve and union arrangement significantly reduces call-backs caused by weeping joints and body stress fractures.

Step 7: Refill, purge and pressure check

7️⃣ Restore water carefully

Close open outlets and slowly reopen isolation valves to refill the system. Purge air from hot and tempered lines via downstream taps. Inspect all joints, unions and valves for leaks under static pressure.

Check pressure conditions. Excessive line pressure or imbalance between hot and cold supplies can cause unstable mixed temperatures. If pressure reduction is required, address this before final commissioning.

Where the system includes check valves or backflow devices, confirm the installation does not create unacceptable thermal expansion conditions.

Step 8: Commission the tempering valve

8️⃣ Set outlet temperature accurately

Allow the hot water system to reach stable operating temperature. Run water through the nearest and furthest relevant sanitary fixtures to stabilise flow and temperature.

Using a calibrated thermometer, adjust the tempering valve to achieve the required mixed outlet temperature, commonly:

Take temperature readings after steady flow is established. Follow the manufacturer’s adjustment method precisely, then lock or cap the setting.

Record:

Step 9: Confirm performance across fixtures

9️⃣ Test the distribution system

Check multiple fixtures downstream of the tempering valve to verify that delivered temperature remains compliant after pipe losses and varying flow conditions. Confirm there is no excessive delay, fluctuation, crossover or pressure imbalance.

If there are long branch runs, dead legs or unusual fixture combinations, verify that the selected valve capacity is sufficient. Re-check after several draw-off events.

💡 A tempering valve set correctly at the plant does not guarantee compliant delivery at every outlet unless the downstream system is tested properly.

Step 10: Finalise, label and hand over

🔟 Complete compliance and documentation

Insulate heated pipework where required and secure all pipe supports. Fit access panels or covers without obstructing future servicing. Label the installation if required by site standards or maintenance protocols.

Provide the owner, builder or facility manager with:

Advise that tempering valves require periodic inspection and may need cleaning, recalibration or replacement depending on water quality and service conditions.

Common Mistakes to Avoid

Pro Tips

Recommended Tools

🔒 Licensing

Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials. For compliance, refer to the relevant regulator including NSW Fair Trading, VIC VBA, QLD QBCC, and WA Building Commission. Gas-adjacent work on gas hot water systems requires a separate gas fitter licence.