AquaMAX hot water: reading the model number, and what the range covers
On the gas range the number is first hour delivery; on the electric range it is the tank. Getting that backwards is how two quotes stop being comparable.
On an AquaMAX gas water heater the number in the model name is not the size of the tank. A G390SS does not hold 390 litres — it holds 155, and 390 is what it can deliver in the first hour from cold. On the electric range the opposite is true: a 250L VE really is a 250 litre tank. That single inconsistency is behind most of the confusion when someone compares a quote for one against a quote for the other, and it is the most useful thing to understand before you replace anything. We sell nothing, install nothing, and have no relationship with the manufacturer.
Who makes AquaMAX?
AquaMAX is owned and manufactured by Rheem Australia, which the brand states on its own site. That matters in a practical way rather than a marketing one: spare parts, owner's guides and warranty administration run through the Rheem organisation, so if you are hunting for documentation on an older unit and the AquaMAX site does not have it, the Rheem archive is the next place to look. The brand has been selling water heaters in Australia since 1988.
It also means a comparison between AquaMAX and Rheem is not the comparison most people think they are making. If you are still deciding what kind of system to put in, the useful question is the type, not the badge — see gas, electric, heat pump or solar, and then what the badge actually decides.
What is in the current AquaMAX range?
Narrower than most brands, and that is the second thing worth knowing. The current catalogue is storage only, in two families:
| Gas storage | Electric storage | |
|---|---|---|
| Cylinder | Stainless steel across the range | Steel lined with vitreous enamel |
| Tank sizes | 130 L and 155 L | 50 L to 400 L |
| Models | Three (G270SS, G340SS, G390SS) | Eleven |
| Siting | Outdoor | Indoor, outdoor or either, by model |
| Cylinder warranty | Up to 12 years on selected models | 5 or 10 years by model |
| Number in the name | First hour delivery | Tank volume |
There is no heat pump, no solar and no continuous flow unit in the current AquaMAX range. If the badge on your wall says AquaMAX and the unit is a solar system or a wall-hung instantaneous heater, it is an older model that is no longer in the catalogue, and the owner's guide archive is where to look it up rather than the current product pages.
Why does a G390SS only hold 155 litres?
Because the gas models are named for first hour delivery: the total volume of hot water the unit can supply in the first hour starting from a full, hot tank. That is the tank plus whatever the burner can reheat while you are drawing off. A gas burner recovers fast — the range is rated to recover up to 185 litres per hour — so a modest tank can out-deliver a much bigger electric one over a morning.
The practical consequence is that tank litres are not comparable across fuel types. Putting "155 L" next to "250 L" on two quotes and picking the bigger number is how people end up disappointed. What you are actually buying is the ability to cover your own peak: how many hot outlets run in the same twenty minutes, and how long the recovery takes before the next one. Our page on what size hot water system you need works through that properly, and the general storage-versus-instantaneous trade-off is covered in instantaneous versus storage.
One more detail that catches people out inside the gas range itself: the largest model carries an inbuilt mixing valve and the middle model does not, which is part of why their first hour figures differ by more than their tanks do. If a plumber is quoting you one instead of the other, that is a fair question to ask about.
Stainless steel or vitreous enamel: does it matter?
It is the difference between the two AquaMAX families, and it is a genuine engineering choice rather than a slogan. The electric range uses a steel cylinder lined internally with vitreous enamel — fired glass — which the manufacturer positions as suiting most water quality types, including the harder water common in regional areas. The gas range uses stainless steel cylinders throughout.
What this does not mean is that one is simply better. A vitreous enamel tank relies on a sacrificial anode to protect the steel, and that anode is a consumable: it is the part that decides whether the tank reaches its warranty or dies early, and whether anyone ever checks it is the single biggest variable in the life of that kind of cylinder. A stainless cylinder is a different corrosion story with different failure modes. Neither survives being ignored for fifteen years, which is the subject of how long a hot water system lasts.
Which AquaMAX do I have, and is it repairable?
Find the data plate: a metal or foil label on the side or front of the unit, usually near the bottom on a tank. It carries the model number, and that number — not the size you remember, not the family name — is what a plumber or a parts counter needs. Photograph it. On the electric range you will see a numeric code such as 991250 or 981125 alongside the capacity; on gas you will see the G-prefixed model.
As to whether it is worth fixing, the answer depends on the fault and not on the brand:
- Usually repairable: a relief valve that has started discharging, a failed thermostat, a failed element on an electric unit, a tempering valve that has drifted, a spent anode.
- Usually terminal: a cylinder that has corroded through and is weeping from the body of the tank itself. There is nothing to repair once the cylinder has gone.
Telling those apart from the outside is harder than it sounds, and getting it wrong is expensive in one direction only — replacing a system that needed a part. Before you agree to anything, which hot water leak is urgent and why the relief valve is discharging are the two pages that separate the cases.
What to have ready before you call
This turns a vague call into a useful one, and it costs you nothing:
- The model number from the data plate, photographed.
- Whether it is gas or electric, and roughly how old.
- Whether the problem affects all hot outlets or only some.
- Where exactly water is appearing: the body of the tank, a fitting, or the relief valve's discharge pipe.
- Whether the relief valve is dripping occasionally or running steadily.
- Any noise the unit did not make before.
- For a replacement quote: how many hot outlets run at once, not how many people live there.
What we will not give you is a number. Prices, running costs, rebates and certificate values change by state, by tariff, by scheme and by year, and a figure written once onto a web page ages into something untrue while still looking authoritative. Get current figures from a supplier and from your own state's energy body.
Where you stop and a licensed plumber starts
Installing, replacing or relocating a hot water system is licensed plumbing work in every Australian state and territory, and each administers it through its own body; the manufacturer says the same thing on its own stockist page. A gas appliance adds licensed gasfitting on top of that.
What you can usefully do is observe and record — the model number, when the symptom started, whether it is all outlets or some, where any water is coming from, and any new noise. What you should not do is open a tank, touch the gas side, or open an electrical enclosure. For where the line sits generally, see what plumbing work needs a licensed plumber.
Frequently asked questions
Does an AquaMAX G390SS hold 390 litres?
No. The G390SS holds 155 litres. On the AquaMAX gas range the number in the model name is first hour delivery — the total hot water the unit can supply in the first hour from a full tank, which is the tank plus what the burner reheats while you draw off. On the electric range the number is the actual tank volume, so a 250L VE really does hold 250 litres.
Who makes AquaMAX hot water systems?
AquaMAX is owned and manufactured by Rheem Australia, as the brand states on its own site, and has been selling water heaters in Australia since 1988. In practice that means spare parts, owner's guides and warranty administration run through the Rheem organisation, which is where to look for documentation on older units.
Does AquaMAX make a heat pump or a solar hot water system?
Not in the current range, which is storage only: three gas models with stainless steel cylinders and eleven electric models with vitreous enamel cylinders. If your unit is badged AquaMAX and is a solar or continuous flow system, it is an older model no longer in the catalogue, and you will need the owner's guide archive rather than the current product pages.
Is a stainless steel tank better than a vitreous enamel one?
They are different corrosion stories rather than better and worse. A vitreous enamel cylinder is steel lined with fired glass and depends on a sacrificial anode to protect it; that anode is a consumable and whether anyone ever checks it largely decides whether the tank reaches its warranty. Stainless cylinders fail differently. Neither survives being ignored for fifteen years.
Can I replace the element in my AquaMAX electric water heater myself?
No. Anything inside the electrical enclosure of an electric water heater — the element, the thermostat, the wiring — is not a homeowner job, and this site does not publish steps for opening one. Installing, replacing or relocating a hot water system is licensed plumbing work in every Australian state and territory.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- AquaMAX (Rheem Australia). AquaMAX gas stainless steel water heaters — current range, first hour capacity and warranty
- AquaMAX (Rheem Australia). AquaMAX electric vitreous enamel water heaters — sizes, cylinder construction and warranty
- NSW Fair Trading. Compliance and regulation — plumbers, drainers and gasfitters