What actually moves the price of a hot water replacement.
Two houses on the same street, the same size unit, and two quotes hundreds of dollars apart. That is not one plumber being greedy. It is seven things found on the day, and the brand on the box is rarely the one that matters most.
The unit is rarely the part that swings the price. The installation around it is. An advertised “installed from” figure assumes the easiest possible version of the job: same type of unit, same position, easy access, and nothing else needing to change.
What actually moves the number is whether you are changing the type of system, how hard the old one is to get out, whether a tempering valve has to go on, whether an electrician or a bigger gas line is needed, and what the valves and pipework look like once the old unit comes off the wall.
Why the advertised price is almost never your price
Every hot water advertisement in the country quotes a best case. The best case is a straight like-for-like swap: a storage unit comes out of an easy spot in the side passage, an identical one goes back in, the existing connections line up, and nothing else needs touching. That job genuinely exists, and when it is your job, the advertised number is honest.
The trouble is that after fifteen or twenty years, most installations have drifted away from that best case. Standards have moved on, the yard has been landscaped around the unit, a deck has been built over the access, or the original install was already a compromise. None of that shows up in an advertisement, and none of it can be known until someone looks.
So the useful question is not “what does a hot water system cost”. It is “which of these seven things applies to me”.
The seven things that move the number
1. Are you changing the type of system?
This is the biggest single swing, by a long way. Storage to storage on the same fuel is the cheap version. Anything else brings new work with it. Gas storage to continuous flow changes the gas requirement and the flue. Electric storage to a heat pump adds electrical work and needs a different position. Gas to electric abandons a gas point and adds a circuit.
2. Where the old one sits, and how hard it is to reach
A unit at ground level beside a gate is one job. The same unit in a first-floor cupboard, in a roof space, behind a fence panel that has to come off, or up a set of stairs with a garden bed in the way is another. Storage units are heavy full and awkward empty, and every extra metre of carrying is time.
3. The base, the stand, or the mounting
Old units often sit on something that has quietly failed: a rusted stand, a cracked slab, or a base that no longer suits the footprint of the new unit. Small on its own, and not optional.
4. The tempering valve
Hot water delivered to fixtures used for personal hygiene in a home has to be limited to a safe temperature, and a tempering valve is what does it. Plenty of older installs predate that requirement and simply do not have one. When the unit is replaced, one goes on. If yours already has a working valve of the right age, nothing changes. If it does not, that is a real line on the quote and it is not negotiable.
5. Electrical work
Heat pumps and some electric units need a licensed electrician, not just a plumber. Depending on what is there now, that can mean a new circuit, a change to the tariff or metering arrangement, or an outlet where there is not one. This is the item that most often surprises people who were expecting a plumbing job and got a plumbing job plus an electrical one.
6. Gas line, flue and clearances
Continuous flow units draw more gas at peak than the storage unit they replace, so the existing gas line is not always big enough. Where it is not, the line has to be upsized, and the length of that run is the cost. Flueing and clearance requirements around a new unit can also force a different position from the old one.
Any gas work also produces a compliance certificate, which we cover in the entry on gas certificates.
7. The valve set, the pipework, and taking the old one away
The relief valve, the cold water expansion control valve, the isolating valve, the drain line: these are consumables that get replaced with the unit rather than reused. Then the old unit has to leave the site and be disposed of properly. Neither item is large, and both are always there.
A failed unit on a Friday afternoon is a different job from a planned replacement. Work outside standard hours carries an uplifted rate, and the choice of unit narrows to whatever can actually be got hold of that day rather than what suits the house best. If your unit is old and behaving oddly, replacing it on your timetable is cheaper than replacing it on its timetable.
Choosing the type: what changes with each
We install Rinnai, Thermann, Quantum and Rheem, and the honest position is that the right choice depends far more on your house and your household than on the badge.
| Type | What it suits, and what it drags in |
|---|---|
| Gas storage | The straightforward like-for-like replacement in a gas home. Cheapest install of the lot when swapping the same for the same. Needs the space the tank takes up. |
| Gas continuous flow | Frees up the footprint and does not run out. Often needs a larger gas line than the unit it replaces, plus flue and clearance work. That gas line is usually the item that decides the price. |
| Electric storage | Simple, and the fallback where there is no gas. Running cost depends heavily on your tariff. Slowest to recover once a household drains it. |
| Heat pump | Cheapest to run of the electric options, and the one attracting government incentives. Needs outdoor space with airflow, needs electrical work, and it is not silent, so position matters more than people expect. |
For a family in Glenmore Park or Jordan Springs with teenagers and a peak-hour shower queue, capacity matters more than anything else. For two people in an older place in St Marys, running cost and install simplicity usually win.
The NSW heat pump incentive, and how it actually reaches you
This one is worth understanding, because it works differently from how most people assume.
Under the NSW Energy Savings Scheme and Peak Demand Reduction Scheme, replacing an existing electric water heater with a heat pump can attract an incentive that NSW describes as typically between $405 and $675. Critically, it is not a rebate paid to you. It arrives as an upfront discount inside the installer’s quote, and only installers partnered with an Accredited Certificate Provider can offer it.
New Energy Security Safeguard rules took effect on 1 July 2026 and changed both schemes, so figures and eligibility quoted in an older article may not hold. Check the current position on the NSW energy site, linked at the bottom of this page.
There is also a minimum five-year warranty against defects requirement for heat pump water heaters at or under 700 litres average insulated storage volume. That is a floor, not a ceiling, and it is worth comparing what each brand offers above it.
Repair or replace?
The blunt version, which most plumbers will tell you privately and fewer will write down:
- Under about eight years and it is a component: usually worth repairing. Thermocouples, valves, elements and thermostats are parts, not the system.
- Over about twelve years and the tank is leaking: replace. A leaking tank is not repairable, and patching around it buys time you do not get.
- In between, and it depends: on how many repairs it has already had, whether parts are still available, and how much longer you intend to be in the house.
Rusty water and no hot water at all are different symptoms with different answers. Water going lukewarm faster than it used to is often an element or thermostat rather than the end of the unit. Full detail is on our hot water page.
What to send us so a quote actually means something
Nobody can give you a real number over the phone from “my hot water is gone”. Four photos and two facts, and we can usually get very close before anyone drives out.
- A photo of the unit from a few steps back, so we can see how it is positioned and what is around it.
- A photo of the compliance plate, the sticker carrying brand, model, capacity and date. That one photo answers half the questions.
- A photo of the pipework and valves where they connect to the unit.
- A photo of the path to it from the street or the gate, so access is not a surprise on the day.
- How many people live there, and roughly when the hot water gets used hardest.
- Whether the house has gas, and whether that is natural gas or bottles.
You get a straight number before anything starts, and if something is found on the day that changes it, you hear about it before it is done rather than on the invoice. A quick look to tell you where you stand is free. Real fault-finding and diagnosis is chargeable, and we will tell you the cost of that first as well. The rules we hold ourselves to are on the promises page.
Common questions
How long should a hot water system last?
Why does the quote include a tempering valve when my old system did not have one?
Is a heat pump actually worth it?
Can you replace it the same day it fails?
Can I buy the unit myself and just pay you to fit it?
My hot water goes cold halfway through a shower. Does the whole thing need replacing?
Where this comes from
The incentive figures and scheme rules below come from the NSW Government, and they get revised. Check the current position before you budget on them.
Written 13 August 2026 and correct against NSW Government guidance on that date. General information for homeowners in our service area, not a quote and not advice on your specific installation. Incentive amounts, eligibility and scheme rules are set by the NSW Government and change.