How to install a new hot water system (electric or gas)

🔧 Installing a New Hot Water System (Electric or Gas) in Australia

What is involved in installing a new hot water system in Australia?

Installing a new hot water system involves safe isolation, removal of the existing unit, correct selection and positioning of the replacement system, compliant connection of water, drainage, electrical or gas services, and full commissioning. 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 Australian installations, work must comply with the PCA, AS/NZS 3500, relevant manufacturer instructions, and state-based licensing requirements such as NSW Fair Trading, VIC VBA, QLD QBCC, and WA Building Commission. Gas work requires a separate gas fitter licence.

What skill level is required to install a hot water system?

Advanced — Estimated time: 4–8 hours for like-for-like changeover, 1–2 days where upgrades, relocations, electrical works, flueing, or gas line alterations are required

What tools are essential for hot water system installation?

What materials are needed for a hot water system installation?

Safety Requirements

Step-by-Step Guide

Step 1: Assess the Existing Installation and Select the Replacement Unit

Inspect the failed or outdated system and confirm the reason for replacement: tank rupture, thermostat failure, burner fault, insufficient capacity, energy upgrade, or compliance issue. Record fuel type, storage volume or flow rate, location, available clearances, pipe sizes, electrical supply, gas meter capacity, flue arrangement, and relief drain discharge path.

Size the new unit to the dwelling or commercial demand profile. For storage systems, review occupancy, peak draw-off, recovery rate, and tariff suitability. For continuous flow gas systems, calculate peak simultaneous demand and fixture flow rates. Where replacing an old electric storage unit with gas or heat-source alternatives, confirm service upgrades and authority requirements.

💡 Match the replacement with the site conditions first, not just the nominal litre rating. A poorly sized unit is one of the most common causes of callbacks.

Step 2: Confirm Compliance Requirements and Site Conditions

Review manufacturer instructions in conjunction with the PCA and AS/NZS 3500. Check whether a safe tray is required, whether seismic or cyclonic restraints apply locally, and whether drainage, access, ventilation, and clearances meet current requirements.

For gas appliances, confirm flueing method, terminal clearances, room ventilation, and gas pipe sizing in accordance with AS/NZS 5601. Check whether tempering is required to sanitary outlets and whether existing valves must be replaced to bring the installation up to standard.

🔒 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. State licensing applies through NSW Fair Trading, VIC VBA, QLD QBCC, and WA Building Commission. Gas work requires a licensed gas fitter.

Step 3: Isolate Services and Drain Down the Existing System

Shut off the cold water inlet to the heater and isolate power or gas. Lock out electrical supply and verify dead before touching any electric unit. For gas, close the appliance gas cock and confirm isolation.

Connect a hose to the drain point if fitted, open a nearby hot tap, and drain the tank. Where no adequate drain point exists, disconnect carefully once pressure is relieved. Be prepared for sediment-heavy discharge on older systems.

⚠️ Safety

Step 4: Disconnect and Remove the Existing Unit

Disconnect hot, cold, relief drain, safe tray drain, electrical conduit, and gas connection as applicable. Remove flue sections from gas storage systems in accordance with safe handling procedures. Cap or seal open services temporarily to prevent contamination or accidental release.

Remove the old unit from the site using appropriate lifting methods. Inspect the base, wall, or platform for corrosion, movement, non-compliant supports, or signs of chronic leakage.

💡 If the previous unit failed due to corrosion, inspect the relief drain termination and inlet control components closely. Chronic overpressure and poor drainage often contribute to premature failure.

Step 5: Prepare the Base, Mounting Area, and Service Connections

Set the new system on a stable, level, compliant base. External units may require a concrete slab or proprietary plinth; wall-hung continuous flow systems require suitable structural fixing. Maintain required service clearances for access, relief valve replacement, burner servicing, and element replacement.

Rough in or alter pipework as needed. Confirm that cold inlet, hot outlet, relief drain, gas line, electrical conduit, and condensate drain locations line up without inducing stress into the appliance connections.

Step 6: Install the Water Services and Control Valves

Connect the cold water inlet with the required inlet control arrangement. Depending on pressure conditions and appliance type, this may include an isolation valve, non-return valve, pressure limiting valve, and expansion control valve. Fit the hot outlet connection and support pipework properly.

Install a tempering valve where required for sanitary fixtures. Run tempered lines to bathrooms and similar outlets as required by code, while kitchen and laundry arrangements should follow local interpretation and design requirements. Insulate external hot pipework and any exposed pipework likely to lose heat.

Typical domestic water connections are commonly in 15 mm or 20 mm copper, but always size to appliance requirements and calculated demand.

Step 7: Install Relief Valve Drain, Safe Tray Drain, and Discharge Pipework

Fit the temperature pressure relief valve supplied or specified for the unit. Run discharge pipework in approved material, continuously graded to drain, terminating in a visible and compliant location. Avoid restrictions, kinks, or undrained low points.

Where a safe tray is required, install it beneath the unit with an independent drain line to an approved discharge point. Ensure the tray drain does not rely on the relief drain and that both remain serviceable and visible where required.

💡 Relief drain workmanship matters. Poorly graded discharge lines are a frequent defect and can create nuisance dripping, corrosion, or concealed water damage.

Step 8: Connect Electrical or Gas Services

For electric storage units, arrange licensed electrical connection to the correct circuit, tariff, isolator, and protection device. Confirm element rating, supply voltage, earthing, and that the tank is filled before energisation.

For gas systems, connect the gas line using approved fittings and isolation. Purge in accordance with safe procedures, pressure-test the line, and verify inlet pressure under operating conditions. Install flue components exactly to manufacturer specification for storage gas units, or terminal components for continuous flow systems. Install condensate drainage where required on high-efficiency models.

Gas pipe sizing must suit the appliance load and installation length. Common branch sizing may start at 20 mm or larger depending on total MJ demand and run length; calculate rather than assume.

⚠️ Safety

Step 9: Fill, Purge, Pressure Test, and Commission the System

Open the cold water inlet and fill the system slowly. Open downstream hot taps to purge air until a steady flow is established. Inspect all water joints under pressure. Test operation of the relief valve and verify there are no leaks from inlet control components, unions, or appliance connections.

For electric systems, once full, energise and verify element and thermostat operation. For gas systems, light and commission in accordance with manufacturer procedure, confirm burner ignition, flame stability, combustion performance where applicable, and outlet temperature.

Check tempered water delivery temperature at the relevant fixtures and adjust the tempering valve accordingly. Verify water pressure, recovery, and discharge function. Record test results as required.

Step 10: Final Compliance Checks, Handover, and Documentation

Complete final checks for access, clearances, support, insulation, valve orientation, drain termination, labeling, and general workmanship. Remove debris and dispose of the old unit in accordance with site and recycling requirements.

Provide the owner or site representative with operating instructions, warranty information, maintenance requirements, and any compliance documentation required in the jurisdiction. Note service intervals, anode inspection intervals for storage tanks where applicable, and expected relief valve testing requirements.

💡 Recommend fixtures with strong water efficiency performance where upgrading the full system. WELS 4-star to 6-star showers and taps can reduce hot water load substantially without compromising performance when pressure is adequate.

Common Mistakes to Avoid

Pro Tips

Recommended Tools