No hot water? What to check first, by system type, and who to call

No hot water: which checks are safe

The quickest way to find the cause of no hot water is to work out whether the unit is getting its energy supply, then whether it is showing a fault. No hot water usually traces back to power, gas, the off-peak heating window or a failed part. Only the first three are things you can check yourself.

The table below sets out the checks in order for each system type found in south-east Queensland homes, and the point where an owner should stop. Each system has its own section further down.

Check this first, whatever hot water system you have

Start by finding out whether the problem is the whole house or one tap, because that tells you whether to look at the hot water unit at all. Run the hot tap in the kitchen, the laundry and a bathroom.

• Hot at some taps but not others: the unit is working. A blocked aerator or shower head can stop one outlet getting hot. Rinnai suggests running two hot taps at once to test this on a continuous flow unit.
• No water at all from hot or cold: the issue is the water supply to the house, not the heater. Check the low water pressure guide.
• Was there a power cut, a storm or water main work today? The unit may need its power cycled or the supply restored before it heats again.
• Look at the unit itself. Note any error code, flashing light, water on the ground or unusual noise. Take a photo of the display and the label with the model number.

That photo of the model label saves time whoever you call. Manufacturers such as Rheem ask for the model number before booking a service.

Electric storage systems: the switchboard, the isolator and off-peak supply

An electric storage tank with no hot water most often has a tripped circuit or is waiting for its off-peak heating window. Go to the switchboard and find the circuit breaker labelled hot water or HWS.

Queensland's Electrical Safety Office says homeowners may reset a circuit breaker or safety switch, but only after checking for a reason it tripped. Reset the hot water breaker once. If it trips again, call an electrician. For a safety switch that trips again after a reset, the Electrical Safety Office says there may be a fault and to seek further advice from your electrician.

Next, check the isolator switch on or near the tank is on. Do not take off any cover on the tank. The element and thermostat sit behind it, and testing or replacing them is electrical work that needs a licence.

Many electric tanks run on a controlled load circuit, which the network operator switches on and off to manage demand, according to Your Home. If the breaker is on and the water is cold, the tank may simply not have had its heating hours yet. Rheem suggests asking your electricity provider to confirm your off-peak times.

Gas systems: check the gas supply, the power and the display

A gas hot water unit with no hot water usually has a gas supply problem, a pilot that has gone out, or an error lockout. Check the supply first.

• LPG bottles: if your home runs on bottled gas, check whether the bottle is empty. Your LPG distributor maintains and tests connected cylinders, and the Queensland Government says to phone your distributor if you have any concerns.
• Natural gas: check the valve at the gas meter is on. Rinnai's own checklist asks owners to make sure the gas valves to the meter and the unit are turned on.
• Power: gas continuous flow units still need electricity. Rinnai lists power, water and gas as the three things its continuous flow units need to run. Check the power point the unit plugs into.
• Error codes: note the code and look it up in the owner's guide. For one ignition code, Rheem tells LPG users to check the bottle level first. Most other codes mean booking a service.

For a gas storage tank, only relight the pilot by following the owner's guide for your model, as Rheem advises. If the pilot won't stay lit, stop. A flame that is unsteady or sputters can mean the gas is running low or the appliance has a fault, says the Queensland Government.

Heat pump and solar systems: boosters, recovery time and weather

A heat pump or solar system with lukewarm or cold water often needs its booster, timer or supply checked rather than a repair. Both systems depend on conditions outside the house, the air temperature for a heat pump and the sun for solar, so the weather plays a part.

Your Home says heat pumps operate more efficiently in warmer, more humid climates. It notes their efficiency drops in colder conditions, and many include a boost element for very cold weather or heavy use. On a heat pump, check the circuit breaker, any timer or app schedule, and whether a fault light is flashing. Rheem says the number of flashing lights on its heat pump controller shows a fault code, and the Owner's Guide for your model explains what each code means.

Solar hot water relies on a booster, electric or gas, when the sun isn't enough. Boosters can be manual or run on a thermostat. After a few cloudy days, check the booster switch is on. If the booster runs on a timer, Rheem says the timer must allow enough time to heat the water your household needs. A gas booster needs its gas supply on, and an electric booster needs its breaker on.

Hot water runs out quickly or is only lukewarm: what it usually points to

Hot water that runs out early, rather than not coming at all, usually points to tank size, tariff timing or a part that has started to fail. On an off-peak tariff, the timing matters most.

Your Home says Tariff 31 (Controlled Load 1) may supply power for 6 to 10 hours a day and Tariff 33 (Controlled Load 2) about 16 to 18 hours. Controlled loads are also being switched on during the day more often, to use excess solar power. Your Home adds that a smaller electric tank may run out before the controlled load circuit switches on to reheat it, and that tanks over 250 litres suit controlled load better. If you run out by the evening and the household or the tariff has changed, the tank may now be too small for its heating window. Our guide to choosing a hot water system covers sizing.

Lukewarm water at every tap can also come from heavy use or a faulty tempering valve, according to Rheem. A plumber tests and replaces that valve. See how tempering valves work. On a gas continuous flow unit, Your Home notes some units shut down at low flow, especially with warm incoming water, and some may not work well with water-efficient shower heads.

Noises, smells or discoloured water with no hot water mean a fault

No hot water that comes with a noise, a smell, a leak or rusty water is a sign of a fault, not a supply problem, so treat it as a job for a licensed plumber. Write down what you notice and when. That detail helps the plumber narrow down the cause.

• Water around the base of the tank: see what to do when a hot water system is leaking.
• Water from the relief valve drain: Rheem says a small release during heating is normal, but more than a bucket in 24 hours may mean a problem.
• Rusty or discoloured hot water: glass-lined tanks rely on a sacrificial anode to reduce corrosion, and Your Home says it needs replacing every few years. Rusty water is worth having checked by a plumber.
• A rotten egg smell near a gas unit: treat it as a gas leak and follow the gas safety steps above.

Who to call: electrician, plumber, gasfitter or supplier

Who fixes a hot water system depends on what has failed, because Queensland licenses electrical, gas and plumbing work separately. Use this table to pick the right call.

Jim Monger Plumbing and Gas handles repairs, replacements and new installations across gas, electric and heat pump units, under QBCC licence 15504687 and gas licence L90908. Call 0418 871 269, or see our hot water repairs and replacements page.

When to stop checking, and what decides repair or replace

Stop checking once you have looked at the supply, the switch and the display and the hot water is still off. Past that point every fix sits inside the unit, and Queensland law reserves that work for licensed trades.

Whether to repair or replace depends on the age of the unit, the part that has failed, the condition of the tank, and whether the system still suits your household and tariff. A leak from the tank body and a failed part on a sound tank are very different decisions, so ask the plumber which one you have. Your Home puts tank warranties at typically 5 to 10 years for glass-lined steel and 10 to 15 years for stainless steel. A warranty is not a lifespan, but an out-of-warranty unit with a failing tank is worth weighing up. Installing a replacement is notifiable work: the QBCC says the plumber lodges a Form 4 within 10 business days and gives you a copy. Homeowners in Victoria Point and across the Redlands can call for a replacement once the decision is made.