Why has your hot water stopped?

These are the causes the troubleshooter works through, ordered the way it orders them: the free checks first, the expensive ones last. A few you can confirm yourself in a minute; the rest tell you what to say when you book someone:

• The circuit has tripped. Look in the switchboard for a breaker labelled hot water, water heater or HWS. Reset it once. If it trips again, stop: a hot water circuit that keeps tripping usually means a failed element, a failed thermostat or moisture in the enclosure.
• It is on a controlled load and has not heated yet. Off-peak systems only heat during set hours. A tank that is cold in the afternoon with the breaker on may simply not have had its window. Or the controlled-load supply may be faulty, which is one for your electricity retailer.
• The cold inlet isolation valve is closed or part closed. There is a valve on the cold inlet to the unit. Recent plumbing work, a filter change or a leak repair can leave it closed, which gives you no hot water while cold works everywhere.
• Failed element or thermostat. The most common electric fault and the most common reason people are told they need a whole new system. A tank with a dead element is otherwise fine.
• The controller has locked out on a fault. Photograph the error code before you cycle the power: it is the single most useful thing you can hand a technician, and it often separates a cheap sensor from a dead compressor.
• Pilot out or ignition failure. The most common gas cause. We do not publish relighting instructions: gas appliance work is licensed gasfitting.
• Tempering valve has drifted or failed. Limits the temperature delivered to bathroom outlets. When it drifts you get lukewarm water at the basin and shower while the kitchen tap is hotter.
• Sediment has reduced the usable volume. Scale builds on the bottom of the cylinder, takes up space and insulates the element. Often arrives together with rumbling noises.
• The system is simply undersized for the household. Nothing is broken. If the hot water has always run out at the same point and the household grew, this is sizing, not a fault.
• Normal expansion discharge from the relief valve. Heated water expands and the temperature and pressure relief valve releases it. A small discharge during a heating cycle is expected behaviour.
• Relief valve discharging continuously. Not normal. Usually high mains pressure with no working pressure limiting valve, debris on the valve seat, or a thermostat letting the tank overheat.
• A fitting, union or valve is weeping. Dry the whole unit with a towel and come back in an hour. If water reappears at a joint first, you have a fitting. Repairable, and nothing to do with the age of the tank.
• The cylinder itself has corroded through. Everything visible stays dry and water still appears at the base, often with rust staining. This is the one condition that genuinely ends a storage system: a pressure vessel that has lost integrity cannot be patched.
• A blockage or partly closed valve on the hot side. If cold pressure is fine everywhere and only hot is weak, the system is usually not the problem. Check the outlet isolation valve, and the aerator or shower rose at the affected outlet.

⚠️ Where the line sits, and it is not a formality. Checking a switchboard breaker, a tap or an isolation valve is yours. Anything inside the unit (element, thermostat, valve, gas) is licensed plumbing work in every Australian state. And on a gas or electric storage heater it is also the part that can scald or electrocute. Knowing the likely cause before you call is worth plenty; opening the unit is worth nothing.

The order is not arbitrary: it runs from free and accessible to expensive and buried. It is the order a good technician works in, and it is the one that stops you replacing a system that needed an element.

Every cause is marked with whether you can check it yourself or whether it is already a trade job. And the ones with a part attached name it so you know what is being replaced. And every symptom ends with a line marked "This far": in Australia most of the repair is licensed work. And the honest thing is to say where that line falls rather than let you find out afterwards.