How to Replace Your Gas Hot Water System: Step-by-Step Guide

Gas hot water systems do not always fail suddenly. There are often warning signs in the weeks or months before complete failure. Recognising these signs gives you time to plan a proactive replacement rather than scrambling for an emergency fix.

Warning signs to watch for:

• Rusty or discoloured water: Brown or rusty-looking hot water coming from taps indicates internal corrosion of the tank. The sacrificial anode has likely been consumed, and the steel tank is corroding. Replacement is not far away.
• Rumbling or banging noises: Sediment build-up at the bottom of the tank creates hot spots that cause the water to boil and produce rumbling sounds. This accelerates tank failure.
• Inconsistent water temperature: If the water runs hot, then cold, then hot again, the thermostat or gas valve may be failing. This is often an early sign of broader system issues.
• Pilot light keeps going out: A pilot light that repeatedly fails may indicate a faulty thermocouple, gas valve, or draft issue. While these are repairable, recurring issues on a system over 8 years old often signal broader wear.
• Visible leaks around the tank: Any water pooling around the base of the tank or dripping from connections indicates seal failure or tank corrosion. A leaking tank is not repairable and requires replacement.
• Age over 10 years: Even without visible symptoms, a gas storage system over 10 years old is approaching end-of-life. Most fail between 8-12 years. If yours is over 10, start planning.
• Higher-than-normal gas bills: A gradual increase in gas usage with no change in household behaviour may indicate declining efficiency from sediment build-up, thermostat drift, or burner degradation.

If you spot any of these signs, do not wait for a complete failure. Get quotes for a heat pump replacement while you still have time to compare options and apply for rebates.

The difference between a planned replacement and an emergency one can be significant in both cost and outcomes.

Planned replacement (recommended):

• Get 2-3 quotes and compare
• Research the best system for your needs
• Apply for Solar Victoria rebate (2-4 weeks wait)
• Schedule installation at a convenient time
• Choose the best installer, not just the first available
• Typical cost: standard pricing with full rebates applied

Emergency replacement (when your system fails):

• Need hot water immediately, so you accept the first available quote
• Limited system selection (whatever is in stock)
• Cannot apply for Solar Victoria rebate in advance (miss $1,000)
• May pay premium for urgent call-out and expedited installation
• Typical cost: 20-30% more than planned, plus missed rebates

The financial impact can be stark. A planned replacement might cost $3,200 after rebates. An emergency replacement of a comparable system might cost $4,500-$5,000 after rebates (if any can be applied in time). That is $1,300-$1,800 in avoidable costs.

If your gas system is approaching 8-10 years old, the smart move is to get quotes now, apply for rebates, and schedule installation for a convenient time in the next few months. You get the best price, the best system, and the least disruption.

A typical gas-to-heat-pump replacement takes 3-5 hours and involves the following steps:

Step 1: Old system removal (30-60 minutes)

• The plumber disconnects the existing gas hot water system from the water and gas supply.
• The old tank is drained and removed. Most installers will dispose of the old unit as part of the installation cost.
• Gas piping is capped off at the isolation point. In most cases, the gas connection to the hot water location is simply capped rather than fully removed from the property.

Step 2: Plumbing connection (60-90 minutes)

• The new heat pump tank is positioned (indoor or outdoor, depending on the system and your preference).
• Hot and cold water connections are made to the new tank.
• The tempering valve is installed or repositioned. This valve mixes stored water (60-65C) with cold water to deliver safe water at 50C to taps.
• For split systems, refrigerant lines are run between the outdoor unit and the tank.

Step 3: Electrical connection (60-90 minutes)

• A licensed electrician installs a dedicated circuit for the heat pump from your switchboard.
• The heat pump is wired to the new circuit, typically a 15-20 amp breaker.
• If using a controlled load tariff, the electrician connects the circuit to the controlled load terminal.
• Timer or smart controller programming is configured.

Step 4: Commissioning (30-45 minutes)

• The system is powered on and the tank begins filling.
• The installer checks for leaks, verifies electrical connections, and tests the heat pump operation.
• Temperature settings and timer schedules are configured.
• The installer walks you through the controller and explains basic operation.

You will be without hot water during the installation (3-5 hours) plus the initial heating period (3-5 hours for the first full heat). Plan for approximately 6-10 hours without hot water from the start of installation to having a fully heated tank. Scheduling for a morning start means you will have hot water by evening.

When you replace a gas hot water system with a heat pump, the gas connection to the hot water location is no longer needed. Here is how it works:

Capping the gas line: The plumber or gas fitter caps the gas pipe at the nearest isolation point, typically where the flexible gas connector met the rigid piping. This is included as part of the standard installation process. The gas line to the hot water location is made safe but not removed from the property.

You keep your gas for other appliances: If you have a gas cooktop, gas heating, or gas fireplace, your gas connection to the property remains active. Only the specific branch to the hot water location is capped.

Full gas disconnection (optional): If the hot water system was your last gas appliance, you may want to consider disconnecting gas entirely. This eliminates the gas supply charge (typically $300-$500/year just for having the connection, even with zero usage). Contact your gas retailer and your distribution network (e.g., AGN, Multinet, AusNet) to arrange disconnection. Note that the meter removal process can take 4-8 weeks.

Financial benefit of full disconnection: If you have already electrified your cooktop and heating, keeping a gas connection just for the supply charge is pure waste. Disconnecting gas can save $300-$500/year in supply charges alone. Over 10 years, that is $3,000-$5,000 saved on top of the running cost savings from switching to a heat pump.

This is the area that catches most homeowners by surprise. Your existing gas hot water system did not need a dedicated electrical circuit (or only needed a small one for electronic ignition). A heat pump requires a proper electrical supply.

What you need:

• Dedicated circuit: A dedicated 15-20 amp circuit from your switchboard to the heat pump location. This cannot be shared with other appliances.
• Circuit breaker: A new RCD-protected circuit breaker in your switchboard.
• Cabling: 2.5mm or 4mm twin and earth cable from the switchboard to the heat pump. Length depends on distance.

Switchboard capacity: This is the potential issue. Older homes (pre-1990) often have switchboards with ceramic fuses and limited capacity. If your switchboard is full or uses old-style fuses, you may need a switchboard upgrade before the heat pump can be connected.

Switchboard upgrade costs:

• Adding a circuit to an existing modern switchboard: $150-$300
• Partial switchboard upgrade (replacing fuses with RCBOs): $500-$800
• Full switchboard replacement: $800-$1,200

A good installer will check your switchboard capacity as part of the quoting process and include any upgrade costs in the quote. If they do not mention your switchboard, ask specifically. You do not want a surprise $800 bill on installation day.

Three-phase power: Most residential heat pumps run on single-phase power. If you have three-phase supply (common in larger homes), this is fine. The heat pump uses one phase. No special requirements.

A gas-to-heat-pump replacement requires at least two licensed tradespeople:

Licensed plumber: Handles the water connections, tank positioning, tempering valve, gas capping, and (for split systems) refrigerant line connections. The plumber must hold a current plumbing licence. For gas disconnection work, they need a gas fitting endorsement.

Licensed electrician: Installs the dedicated circuit, connects the heat pump to power, programs timers, and issues a Certificate of Electrical Safety. Must hold a current electrical licence.

Most heat pump installers are plumbing businesses that either have an electrician on staff or subcontract to one. When you get a quote from a heat pump installer, it should include both the plumbing and electrical work as a single price.

What about permits?

• Plumbing compliance: The plumber will lodge a plumbing compliance certificate with the VBA (in Victoria) or equivalent regulator. This is standard practice and included in the installation.
• Electrical safety certificate: The electrician issues a Certificate of Electrical Safety. You should receive a copy.
• Building permit: Not required for a like-for-like hot water system replacement in most Australian jurisdictions. If the installation involves structural changes (e.g., a new concrete slab for the tank), check with your local council.
• Planning permit: Not required for standard residential heat pump installation. Heat pumps are classified as "exempt" minor buildings/works in most planning schemes.

Most heat pump installations go smoothly, but here are the issues that occasionally crop up and how to handle them:

1. Switchboard surprise: As discussed above, older switchboards may need upgrading. Get this checked at the quoting stage. If the installer has not inspected your switchboard, ask them to.

2. Access difficulties: Heat pump tanks are heavy (60-80kg empty for a 315L unit). If the installation location is up stairs, through narrow doorways, or in a tight space, additional labour may be required. Mention any access challenges when requesting quotes.

3. Noise placement: Positioning the outdoor unit too close to a bedroom window or a neighbour's boundary can cause complaints. Council noise regulations typically require outdoor equipment to be below 45 dB at the property boundary. Discuss placement with your installer and measure distances to boundaries.

4. Drainage requirements: Heat pumps produce condensate (like an air conditioner) during operation. The outdoor unit needs a drain point or connection to stormwater. If there is no existing drainage nearby, the installer will need to run a condensate line.

5. Hot water pipe insulation: Insulating the hot water pipes between the tank and your taps reduces heat loss and improves efficiency. Good installers include pipe insulation as standard; cheaper ones may not. Ask if pipe insulation is included in the quote.

6. WiFi connectivity: Some newer heat pumps (Stiebel Eltron, newer Rheem models) have WiFi controllers for remote monitoring. If you want this feature, ensure your WiFi reaches the installation location. A WiFi extender may be needed for outdoor installations far from the router.

Here are practical ways to reduce the cost of replacing your gas hot water with a heat pump:

1. Get 3 quotes, minimum. Prices vary significantly between installers. We have seen quotes for the same system range from $3,800 to $5,500 installed. The difference is often margin and overhead, not quality. Use a service like PumpSwap's free quote comparison to streamline this.
2. Stack every rebate. Do not leave money on the table. Federal STCs ($500-$700) + Solar Victoria ($1,000) + VEU certificates ($700-$1,000) can save up to $2,700 in Victoria. Check your eligibility for all available programs.
3. Apply for Solar Victoria before installation. The rebate must be approved before work begins. Allow 2-4 weeks for processing.
4. Replace proactively, not reactively. Emergency replacements cost 20-30% more and you miss the Solar Victoria pre-approval window. If your system is 8+ years old, plan now.
5. Choose the right size, not the biggest. Do not over-specify. A 315L system costs $300-$500 more than a 270L. If 270L covers your household needs, choose the smaller option.
6. Bundle electrical work. If your switchboard needs an upgrade, or you have other electrical work needed (new power points, smoke alarm upgrades), doing it all at once saves on call-out fees.
7. Consider timing. Summer and early autumn (Dec-Mar) can be quieter periods for hot water installers. You may find better availability and occasionally promotional pricing outside the peak demand season (winter).
8. Disconnect gas if it is your last appliance. If you no longer use gas for anything, disconnecting saves $300-$500/year in supply charges. This alone covers a significant portion of the heat pump running cost.