Hot Water System Troubleshooting, Symptom by Symptom

There's no single most common hot water fault, because the likely cause depends on the system. A tripping safety switch means something different on an electric tank than a flashing code does on a heat pump, so name the system before you read anything else.

Home hot water systems come in five main types. An electric storage tank is a tall cylinder with no flue and no fan. A gas storage tank looks similar but has a flue on top and a gas line at the base. A gas continuous flow unit is a slim box on an outside wall with no tank at all. A solar system has collector panels on the roof and a tank on the roof or the ground, usually with an electric or gas booster. A heat pump is a tank with a fan and a compressor on top or beside it, a little like an air conditioner.

Then find the data plate, the label on the side of the unit. Rheem asks owners for the model number, serial number and date of manufacture when checking a warranty, and for the model number when a fault code shows. Take a clear photo of the plate now, so those details are ready when you call.

When the cold works and the hot doesn't, the first check is whether the system has power or gas. On an electric tank or heat pump, look at the switchboard for a tripped safety switch or circuit breaker on the hot water circuit. If the switch trips again, or will not stay on, leave it off. The Electrical Safety Office says a safety switch that won't reset may mean a fault on the circuit that needs a licensed electrician.

An off-peak electric tank only heats at set times, because Rheem notes these heaters are connected to a timed tariff. A big day of showers and washing can empty it until the next heating window, so no hot water in the evening is not always a fault.

On gas, check the LPG bottle has gas and the valve is open. For an ignition failure code on its continuous flow units, Rheem tells LPG users to check the bottle, cycle the power once at the power point, and book a service if the code comes back. Some manufacturers publish pilot relighting instructions for owners; follow only the steps in your own owner's guide. For a fault code on its solar and heat pump systems, Rheem points owners to the owner's guide for that model.

The source of the leak matters more than its size. Water from the relief valve drain line can be normal, which the next section covers. Water at a pipe joint or valve is usually a part that can be repaired. Water coming from the tank body itself, or rust weeping down the casing, means the cylinder has failed, and a failed cylinder is a replacement rather than a repair.

What you can do safely: keep people and pets clear, turn off the cold water isolating valve to the system if you can reach it easily, and switch the hot water circuit off at the switchboard or turn the unit off at its gas control as the owner's guide shows. Take photos of where the water is coming from before you mop up.

Replacing the system is notifiable work in Queensland. The QBCC lists replacement of hot water heaters as notifiable work, and the licensed plumber who does it must lodge a Form 4 with the QBCC within 10 business days. Ask for a copy of that notice for your records.

A relief valve that drips while the tank heats is doing its job. Rheem describes some discharge during the heating cycle as normal and desirable, because water expands as it warms, and puts the amount at roughly one fiftieth of the hot water you use.

The warning sign is volume. According to Rheem, a valve that discharges more than a bucket of water in 24 hours may point to another problem. A valve that runs steadily, day and night, needs a plumber.

The QBCC says home owners and tenants can operate the temperature pressure relief valve lever themselves, with care to avoid scalding and to make sure the valve closes properly afterwards. That is the limit. Never block, cap or tie off the drain line, and never remove or adjust the valve. Replacing it is plumbing work that needs a licence.

Lukewarm water usually comes down to how much is being used, a booster that isn't doing its share, or a valve cooling the water too far. Rheem lists heavy hot water use and a faulty tempering valve that over-cools the water as two common causes.

On solar, Rheem's advice is to check that the booster is being used the way the installation instructions for your model say, and that any booster timer allows enough time to heat the water your household needs. On gas continuous flow, temperature that swings between hot and cold usually means the flow is too low to keep the unit firing. Rheem names flow restrictors and water-saving low-flow taps as causes, and a plumber can raise the flow to at least two to three litres a minute.

Don't turn a storage thermostat down to fix comfort. Rheem says stored water needs to sit at a minimum of 60 degrees for showers to work properly, and the QBCC links that same temperature, held over 24 hours, to limiting Legionella. Tempering valves need regular servicing in line with the manufacturer's instructions, and a thermostatic mixing valve must be serviced by a licensed plumber with the right endorsement.

A hot water system that trips the safety switch points to an electrical fault, and repeated resetting is not a fix. The Electrical Safety Office explains that safety switches cut the power when they detect current leakage, which is exactly the situation they exist to stop. On an electric storage tank, a common cause is a failed heating element.

The repair itself is electrical work. Under Queensland's Electrical Safety Act, electrical work includes testing, repairing, removing and replacing electrical equipment, so an element or thermostat swap is not an owner job. The Electrical Safety Office states that DIY electrical work is illegal, with penalties of up to $40,000 for individuals, and that an insurer may refuse a claim for fire damage caused by illegal electrical work.

Leave the hot water circuit off, keep the cover on the unit, and book a licensed tradesperson. Ask whether they hold the electrical licence for the disconnection and reconnection side, so the job doesn't need a second trade and a second visit.

Treat any gas smell near a gas hot water system as a safety issue first and a hot water problem second. Fuel gas has mercaptan added to give it a rotten egg smell so leaks are noticed. The Queensland Government's gas safety steps are: don't light anything and don't switch electrical devices or lights on or off, turn the gas appliance off, and open doors and windows. If you can still smell gas, turn off the gas supply and contact your gas supplier or a gasfitter. If the smell remains after the supply is off, call 000.

The same page says to contact a gasfitter if the igniter doesn't light within a few clicks, or if the flame is unsteady or sputters. Owners can look over the system for corrosion, deterioration or damage, and keep anything flammable away from it.

New noises, a burning smell, or discoloured or smelly hot water have several possible causes, and none of them are owner fixes. Note when it happens, whether it is hot water only or cold as well, and whether it comes from every tap or just one. Those three details tell a plumber a lot before they arrive.

Most work on a hot water system needs a licence in Queensland, and the line sits closer to the owner than many people expect. The QBCC states that most plumbing work in Queensland is regulated and needs a QBCC licensed plumber. The work an owner may do without a licence is a short list, such as changing a shower head, replacing a water filter or replacing a tap washer. Repairing or replacing anything on the tank, its valves or its pipework is licensed work.

The gas side belongs to a licensed gasfitter. The Queensland Government says only a licensed gasfitter can carry out gas work, which includes installing, repairing, servicing and testing the gas system and its connections. The wiring side belongs to a licensed electrician or a tradesperson holding the appropriate electrical licence. Solar and heat pump installation also needs an endorsement on the plumber's licence, according to the QBCC.

The QBCC also makes the owner responsible: a home owner must take all reasonable steps to keep the property's plumbing compliant, and the simplest way is to use a licensed person and ask to see their licence card. Rheem's guidance fits the same line from the manufacturer's side: owners do only the basic maintenance their owner's guide lists for owners, and repairs go to a plumber.

A short, specific description helps the plumber bring the right parts. Before you call, gather these:

The system type and brand, plus a photo of the data plate showing the model and serial number. Roughly how old the system is, if you know. The symptom and when it started, and whether it is constant or only at certain times of day. Any error code on the display, written down exactly. What you have already checked, such as the switchboard, the gas bottle or the relief valve. Photos of any leak, taken before you clean it up. Whether the system runs on mains gas or an LPG bottle, and whether the house is on town water, rainwater or bore water.

The water source matters more than people think. The QBCC notes that systems on bore water or rainwater may need servicing more often than its general guide of a service every five years by a licensed person. If you rent, contact your property manager or the owner first and send them the same photos so they can brief a plumber properly.