Buying a Second Hand or Ex-Display Hot Water System: What to Check Before You Hand Over Cash

There is a real second hand hot water market in Australia, and it is not all junk. Renovations pull out systems that are barely two years old. Builders end up with surplus stock. Retailers clear ex-display and slightly damaged boxes. Solar and heat pump upgrades leave behind perfectly serviceable gas units. On the other side of the same market sit tanks that were removed precisely because they were about to fail, listed by someone who would rather you found that out at your place than theirs.

The difference between those two piles is almost always visible before money changes hands, if you know what to look at. Here is the inspection, in the order it is worth doing.

Read the data plate before you read the ad

Every hot water system carries a compliance and rating plate, usually on the outer jacket or the control cover. It is the single most useful object in the transaction, because it tells you what the seller may not.

You are looking for the model number, the serial number, the capacity in litres or the flow rating, the energy input, and for gas units the gas type. Photograph it. From the model and serial you can usually establish the manufacturing date, because most Australian brands encode a year and week or month in the serial. If a seller will not send a clear photo of the plate, that is the end of the conversation. There is no innocent reason to hide it.

Gas type matters more than people expect. A natural gas unit is not an LPG unit and converting between them is not a matter of a fitting. If you are on bottled gas and the plate says natural gas, walk away regardless of price.

Establish the age honestly

Ask directly how old it is and when it was installed, then check that against the plate. A tank's practical life is finite and it is mostly determined by corrosion, so a cheap ten-year-old tank is not cheap, it is a removal job you are paying to acquire.

Electric and gas storage tanks are the highest risk purchase second hand, because the expensive failure, the inner cylinder, is the one part you cannot inspect. Continuous flow units and heat pumps carry less of that risk because there is no large stored volume of hot water sitting against steel, though they carry their own, which is electronics and compressors.

The genuinely low-risk buys are ex-display units, surplus new stock, and systems removed intact from a renovation within the first few years of life. Those turn up regularly across hot water listings and are worth watching for rather than chasing.

Inspect the tank itself

Get it in daylight and walk around it. On a storage system, look for rust weeping from the bottom skirt, staining down the jacket, a swollen or distorted outer casing, and any sign of water tracking from the seams. Rust at the base of a tank is the classic tell, and it usually means the inner cylinder has already gone. A tank that has been sitting in a yard for a year with the fittings open has had air and moisture in it and should be priced as scrap.

Ask whether the sacrificial anode has ever been checked or replaced. Almost nobody will say yes, but the answer tells you something either way, and it is the single best predictor of remaining tank life. If you are buying a tank at all, understanding what the anode does is what turns a gamble into a calculated one, and budgeting for a fresh rod on installation day is sensible on anything that is not brand new.

On a heat pump, look at the evaporator fins for crush damage and corrosion, spin the fan by hand for roughness, and check that the unit has not been laid on its side in transport, which some manufacturers specifically prohibit. On a continuous flow unit, open the front cover if the seller allows and look for water staining inside the case, corroded burner components, and evidence of rodents, which are a surprisingly common cause of death in outdoor units.

Check the valve gear, and price in replacing it

The valves are cheap relative to the system and they are the parts that make it safe, so treat them as consumables rather than inclusions.

The pressure and temperature relief valve on a storage system is a safety device with a service life. On any used tank, plan on a new one. A seller telling you the old one is fine is not a warranty, and the consequences of a stuck PTR are not proportionate to the saving. If the valve on the unit has been capped, plugged or plumbed into something odd, treat that as a serious warning about the whole system's history, and read what a dripping PTR valve is actually telling you before you install anything.

The same goes for the tempering valve, which is what limits water at your bathroom outlets to a maximum of 50 degrees. It is a wear item, it will not be transferable in any meaningful sense, and a new install needs a correctly rated one anyway. Both valve types are easy to source under valves and relief listings.

While you are there, ask what has been done to the system. A tank that has had a new element at some point is not a bad thing, it is a maintained tank, and elements and thermostats are cheap and available under elements. A tank that has had three elements in four years is telling you the water is aggressive or the element is undersized for the duty.

Warranty, paperwork and the install reality

Manufacturer warranties on hot water systems are commonly tied to the original purchaser and to a compliant installation by a licensed tradesperson. Assume a second hand purchase carries no warranty at all unless the seller can produce documentation and the manufacturer confirms transfer, which is rare. Price accordingly.

Then price the install. This is where second hand deals quietly fall apart. In Australia, installing a hot water system is licensed plumber work, and anything involving gas is licensed gasfitter work. A licensed plumber is putting their name on the job, and some will decline to install a customer-supplied used unit, particularly a gas one, because they carry the liability for it. Ask before you buy, not after. The directory of hot water plumbers is the place to line that conversation up early.

Also check the practical fit: physical dimensions and whether it goes through the door and into the space, connection positions, electrical supply and whether a controlled load circuit exists, and for heat pumps a condensate drain and clearances for airflow.

Red flags worth walking away from

A refusal to show the data plate. No clear answer on age. Rust at the base of a tank. A capped or modified relief line. A gas unit with the wrong gas type for your property. A heat pump or continuous flow unit that cannot be powered up for a basic function check. And the general one: a seller who is vague about why it came out. "Upgraded to solar" and "renovation, wrong colour cabinetry" are ordinary answers. Silence is not.

If you have your own system to move on, listing it honestly with clear plate photos is exactly what gets it sold quickly, and you can list it here. And if you are still deciding which technology you want in the first place, work through the comparison of electric, gas, heat pump and solar before you start hunting bargains, because the cheapest system you can find is rarely the cheapest system to own.