Common Hot Water Terms Explained

TankA storage system heats and stores water in an insulated tank until it's needed. Common in Sydney homes and available in electric, gas and solar. Tank size (typically 50 L–400 L) determines how much hot water you have before it needs to reheat. Available in single or twin (double) element.

InstantA continuous flow (instantaneous) heater heats water only when a tap is turned on, so you never run out. Compact and energy-efficient, they're rated by how much water they heat per minute — e.g. 26 L/min — and suit households with high hot water demand.

RequiredA tempering valve mixes hot water from the tank with cold water to deliver it to your taps at no more than 50°C, reducing the risk of scalding. Required under AS/NZS 3500 and must be fitted to any tank replacement.

SolarSolar systems use heat from the sun to warm your water. Two main types: Lowline (tank on the ground, panels on the roof) and Highline (all components on the roof). Most include a gas or electric booster for when solar gain isn't enough.

Leak protectionUnder AS/NZS 3500, water heaters installed indoors in concealed or non-wet areas (no floor drain) need a safety drip tray plus either a drain or an approved leak-protection / automatic shut-off valve. We install devices such as the Mildred shut-off valve, the AVG eFlow stop valve, and the Thompson leak-detection valve — each uses a sensor that detects water in the tray and automatically shuts off the supply to the system, protecting your property from costly water damage.

IsolationA duo valve combines two functions in one: a stop tap (to shut off water flowing into the heater) and a non-return valve (to stop hot water flowing back down the cold pipe). It lets you quickly isolate the hot water supply in an emergency or for plumbing work.

Relief valveWater discharging from the pressure/temperature relief valve usually means the system is releasing excess pressure or heat — occasional dripping can be normal. Constant leaking, however, may point to a faulty valve or a pressure problem and should be checked by a licensed plumber.

ElectricAn electric hot water system uses one or two heating elements inside the tank to warm the water. They're reliable, simple to install and ideal where gas isn't available. Running on an off-peak electricity tariff can significantly reduce running costs. Available in a range of tank sizes to suit any household.

GasA gas hot water system heats water with a gas burner — available as both storage tanks and continuous flow units. Gas heats water faster than electric and isn't affected by electricity tariffs, making it a popular, cost-effective choice for homes connected to natural gas or LPG.

Energy efficientA heat pump works like a reverse fridge — it draws warmth from the surrounding air to heat your water, using up to 60–70% less electricity than a standard electric system. They're one of the most energy-efficient options available and may qualify for government rebates.

Tank protectionAn anode is a metal rod inside the tank that corrodes instead of the steel tank — "sacrificing" itself to prevent rust. Over years it wears away, and once it's gone the tank starts to corrode. Replacing the anode periodically can significantly extend the life of a storage system.

SafetyThe PTR valve is the main safety device on a storage tank. It releases water if pressure or temperature climbs too high, preventing the tank from over-pressurising. It's normal to see occasional dripping — but constant discharge means the valve or system pressure should be checked by a licensed plumber.

Pressure controlFitted to mains-pressure systems, the expansion control valve relieves the extra pressure created as water heats and expands. It takes the strain off the tank and PTR valve, helping the system last longer. In many areas it's required to keep your installation compliant.

MaintenanceHard water carries dissolved minerals that build up as sediment and scale inside the tank and on the element over time. This reduces efficiency, causes rumbling noises and can shorten the system's life. Periodic flushing helps keep things running well.

GasOn older gas systems, the pilot light is a small constant flame that ignites the main burner when hot water is needed. If it goes out, you'll have no hot water. Many modern gas units use electronic ignition instead, removing the pilot light altogether.

Electric partsThe element heats the water (like a giant kettle element) and the thermostat controls the temperature and switches the element on and off. These are the two most commonly replaced parts on an electric system — a faulty element or thermostat is a frequent cause of "no hot water."

PerformanceRecovery rate is how quickly a system reheats a tank of water after it's been used. A faster recovery rate means less waiting for hot water to come back. Gas systems generally recover faster than electric, which is worth considering for busy households.

EfficiencyThe energy star rating shows how efficient a system is — more stars means lower running costs. kW (kilowatts) measures how much power a unit draws or how much heat it produces. Higher-efficiency systems like heat pumps and good-rated gas units cost less to run over time.

Tank typesMains-pressure systems deliver hot water at the same strong pressure as your cold taps — the most common type today. Constant/low-pressure (gravity-fed) systems run at reduced pressure and are usually found in older homes. The type affects flow, valves required, and which replacement units suit your home.