How to service a gas hot water system
This guide outlines the essential steps for servicing a gas hot water system, focusing on routine maintenance to ensure safe, efficient, and compliant operation. Regular servicing helps prolong the life of the unit, maintain energy efficiency, and prevent potential hazards. This task is critical for
- Skill level
- Intermediate
- Time
- 1-2 hours
- Trade
- Plumbing
- Updated
- 4 November 2026
Tools you will need
- Adjustable spanners
- Pipe wrenches
- Multimeter: To test electrical components
- Pressure gauge
- Bucket
- Hose
- Wire brush: For cleaning burner assembly.
- Screwdrivers
- Safety glasses: Essential for eye protection.
- Gloves
What is involved in servicing an Australian gas hot water system?
This guide outlines the essential steps for servicing a gas hot water system, focusing on routine maintenance to ensure safe, efficient, and compliant operation. Regular servicing helps prolong the life of the unit, maintain energy efficiency, and prevent potential hazards. This task is critical for both residential and commercial installations.
What skill level is required to service a gas hot water system in Australia?
Intermediate — Estimated time: 1-2 hours
What specific tools are required for servicing an Australian gas hot water system?
Adjustable spanners (200mm & 300mm): For various fittings and connections. Pipe wrenches (300mm & 450mm): For larger pipe work and sacrificial anode removal. Multimeter: To test electrical components (e.g., thermocouple, gas valve). Gas leak detector spray or electronic gas sniffer: For identifying gas leaks. Pressure gauge (0-1000 kPa): To check water pressure. Temperature gauge: To verify hot water outlet temperature. Bucket (10-20L capacity): For draining water. Hose (garden variety): For draining the tank. Wire brush: For cleaning burner assembly. Screwdrivers (flathead & Phillips): For access panels and various fasteners. Safety glasses: Essential for eye protection. Gloves (heat resistant and general purpose): For handling hot components and general protection. Torch/inspection lamp: For inspecting internal components. Small mirror: To inspect hard-to-reach areas. Vacuum cleaner (shop vac): For cleaning dust and debris.What materials are essential for servicing a gas hot water system in Australia?
Sacrificial anode: Magnesium or aluminium, specific to the hot water system make and model (e.g., 25mm or 32mm thread). PTFE thread tape (gas rated): For sealing gas connections. Thread sealant (gas rated): For sealing gas connections. New thermocouple (if required): Specific to the hot water system make and model. New pressure and temperature relief valve (PTRV) (if required): Rated for the system's pressure and temperature (e.g., 700 kPa, 99°C). New tempering valve (if required): AS 4032.2 compliant, set to 50°C for domestic hot water. Cleaning rags/wipes.Safety Requirements
⚠️ Safety is paramount when working with gas and hot water systems.
ALWAYS turn off the gas supply at the main meter or appliance isolation valve before commencing work. ALWAYS turn off the electrical supply (if applicable) at the main switchboard or appliance isolation switch. ALWAYS allow the hot water system to cool down before draining or working on internal components to prevent scalding. ALWAYS wear appropriate Personal Protective Equipment (PPE), including safety glasses and gloves. NEVER attempt gas work unless you are a licensed gas fitter. This guide is for licensed professionals. ENSURE adequate ventilation when working with gas appliances. CHECK for gas leaks thoroughly after any gas connection has been disturbed or reconnected. 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.Step-by-Step Guide
Step 1: 1️⃣ Isolate Services and Conduct Initial Inspection
Turn off the gas supply to the hot water system at the isolation valve or main meter. Turn off the cold water supply to the unit. If the unit has an electrical supply (e.g., for electronic ignition), turn this off at the switchboard. Visually inspect the unit for any obvious signs of leaks, corrosion, damage, or unusual noises. Check the flue for blockages or damage. Note the age of the unit and the last service date.
Step 2: 2️⃣ Drain the Hot Water Tank
Connect a garden hose to the drain valve at the bottom of the hot water tank. Run the hose to a suitable drain point. Open the drain valve and open a hot water tap inside the house (or the PTRV lever) to break the vacuum and allow the tank to drain completely. This flushes out sediment that has accumulated at the bottom of the tank. Allow sufficient time for the tank to cool before proceeding.
Step 3: 3️⃣ Inspect and Test the Pressure and Temperature Relief Valve (PTRV)
With the tank drained, carefully lift the lever on the PTRV for a few seconds to ensure it operates freely and discharges water (if the tank was still pressurised). Release the lever. If the valve sticks, leaks continuously, or does not discharge, it must be replaced. Check the discharge pipework for blockages or damage. The discharge pipe must terminate safely and visibly, as per AS/NZS 3500.4.
Step 4: 4️⃣ Replace the Sacrificial Anode
Locate the sacrificial anode, usually found at the top of the tank, often under a plastic cap or next to the hot water outlet. Using a large pipe wrench or spanner, carefully unscrew the old anode. Inspect its condition; if it's less than 25% of its original diameter, it needs replacement. Clean the thread, apply new PTFE thread tape and thread sealant, and install the new anode, tightening it securely but not over-tightening.
Step 5: 5️⃣ Inspect and Clean the Burner Assembly
Access the burner compartment (usually at the bottom of the unit). Carefully remove the burner assembly. Use a wire brush to clean any soot, dust, or debris from the burner ports and pilot light assembly. Inspect the heat exchanger for any signs of corrosion or blockages. Use a vacuum cleaner to remove any loose debris from the combustion chamber. Ensure all air inlets are clear.
Step 6: 6️⃣ Inspect and Test Thermocouple/Flame Sensor
Inspect the thermocouple or flame sensor for corrosion or damage. If the pilot light frequently goes out, or the main burner doesn't ignite reliably, the thermocouple may be faulty. Test the thermocouple's millivolt output with a multimeter (should be around 20-30mV when heated). Replace if faulty. Ensure it is correctly positioned in the pilot flame.
Step 7: 7️⃣ Reassemble, Refill, and Test for Leaks
Reassemble the burner compartment. Close the drain valve. Reopen the cold water supply valve to the hot water system. Open a hot water tap inside the house to purge air from the system. Once water flows steadily from the tap, close it. Inspect all water connections for leaks.
Step 8: 8️⃣ Restore Gas Supply and Test Operation
Slowly turn on the gas supply. Use gas leak detector spray or an electronic gas sniffer on all gas connections that were disturbed. If no leaks are detected, light the pilot and then turn on the main burner. Observe the flame; it should be blue and steady, with no yellow tipping. Check the hot water outlet temperature with a thermometer after the unit has heated up, ensuring it's within safe limits (e.g., 50°C at the tap for domestic hot water via a tempering valve).
Step 9: 9️⃣ Check Tempering Valve (if fitted)
If a tempering valve is fitted, check its operation. Measure the hot water temperature at a designated outlet (e.g., bathroom basin). It should be no more than 50°C for domestic hot water. If the temperature is incorrect or fluctuates, the tempering valve may need adjustment or replacement. Refer to AS 4032.2 for correct installation and testing procedures.
Common Mistakes to Avoid
Pro Tips
💡 Educate the client: Explain the importance of regular servicing, especially anode replacement, to extend the life of their unit. 💡 Check flue integrity: A blocked or damaged flue can lead to carbon monoxide poisoning. Always ensure it's clear and correctly installed. 💡 Water quality assessment: In areas with hard water, consider recommending a water filter or more frequent descaling. 💡 WELS rating check: For new installations or replacements, always recommend units with high WELS ratings for water efficiency. 💡 Document everything: Keep detailed records of service dates, parts replaced, and any observations for future reference.Recommended Tools
Ridgid 31095 18-inch Aluminium Pipe Wrench: Lightweight and durable for anode removal. Testo 316-1-EX Gas Leak Detector: Reliable electronic sniffer for accurate leak detection. Fluke 117 True RMS Multimeter: Essential for accurate electrical diagnostics of thermocouples and gas valves.Frequently asked questions
- What is involved in service a gas hot water system?
- This guide outlines the essential steps for servicing a gas hot water system, focusing on routine maintenance to ensure safe, efficient, and compliant operation. Regular servicing helps prolong the life of the unit, maintain energy efficiency, and prevent potential hazards. This task is critical for
- What skill level do I need for service a gas hot water system?
- Intermediate — Estimated time: 1-2 hours
- What are common mistakes when service a gas hot water system?
- 1. Not fully isolating services: Failing to turn off gas and water supplies can lead to dangerous leaks or scalding. 2. Ignoring the sacrificial anode: This is the most common cause of premature tank failure. Neglecting replacement leads to tank corrosion. 3. Over-tightening fittings: Especially with gas connections, over-tightening can strip threads or damage components, leading to
- What tools do I need for service a gas hot water system?
- This guide includes a comprehensive tools list. Key plumbing tools are detailed in the Tools Required section.
- What is involved in servicing a gas hot water system?
- Servicing a gas hot water system involves routine maintenance to ensure safe, efficient, and compliant operation, as outlined in AS/NZS 5601.1. This includes checking gas connections, testing safety devices like the PTRV, inspecting the burner, and replacing the sacrificial anode. Regular servicing, typically every 1-2 years, helps extend the unit's lifespan and prevents costly breakdowns.
- What skill level do I need for servicing a gas hot water system?
- An intermediate skill level is required for servicing a gas hot water system, as it involves working with gas and high-pressure water systems. This task should only be performed by licensed plumbers or gasfitters in Australia, in accordance with state-specific regulations and AS/NZS 5601.1. Estimated time for a comprehensive service is 1-2 hours.
- What are common mistakes when servicing a gas hot water system?
- Common mistakes include not fully isolating gas and water supplies, which is a significant safety hazard. Another frequent error is neglecting the sacrificial anode replacement, leading to premature tank corrosion and failure. Over-tightening gas fittings can also cause damage or leaks, contrary to AS/NZS 5601.1 guidelines for proper torque.
- How often should a gas hot water system be serviced in Australia?
- According to manufacturer recommendations and best practice, a gas hot water system in Australia should be serviced annually or biennially (every 1-2 years). This frequency ensures optimal performance, safety compliance with AS/NZS 5601.1, and helps identify potential issues like a depleted sacrificial anode before they cause significant damage or inefficiency.
- Why is the sacrificial anode important in a hot water system?
- The sacrificial anode is crucial because it protects the hot water tank from corrosion by attracting corrosive elements in the water, sacrificing itself in the process. Neglecting its replacement, typically every 3-5 years depending on water quality, is the leading cause of premature tank failure in Australia, as confirmed by industry bodies like the Australian Gas Association (AGA).
Written by Pipey, the Plumbing specialist at Aus.Tools.