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No hot water: what to check, in order

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The cause is usually one of six things, and which six depends on whether your system is electric, gas or a heat pump. Two of them you can check in five minutes without tools.

"No hot water" is not one fault. Before anything else, establish which of these you have, because they lead to completely different places:

  • No hot water anywhere, cold water fine — the heat source has stopped. This page.
  • Hot water at some taps but not others — not the system; a tap, a mixer cartridge or an isolation valve.
  • Hot water that starts hot then goes cold quickly — the system is heating, but not enough of the tank is hot. Usually a failed lower element or an undersized tank.
  • No water at all, hot or cold — supply, not hot water. Check a cold tap and your stop tap.

First, work out what you actually have

Go and look at the unit. You are checking three things: is it inside or outside, does it have a tank, and is there a gas line or an electrical circuit going to it.

  • A tank with an electrical cable and no flue: electric storage.
  • A tank or wall unit with a gas line and a flue or vent: gas.
  • A tank with a boxy unit on top or beside it that looks like an air conditioner, and makes a fan noise when running: heat pump.
  • Panels or evacuated tubes on the roof feeding a tank: solar thermal, which will also have an electric or gas booster.
  • A small wall unit with no tank that only runs while a hot tap is open: continuous flow.

The checks that are yours to make

1. Has the circuit tripped? (electric and heat pump)

Electric storage systems are usually on their own circuit, and very often on a controlled or off-peak tariff with its own switch. Look in the switchboard for a breaker labelled hot water, water heater or HWS. If it has tripped, that is information, not a fix: a breaker that trips on a hot water circuit usually means the element or thermostat has failed and is drawing current it should not, or moisture has got in. Reset it once. If it trips again, stop and get an electrician or plumber — a circuit that keeps tripping is doing its job.

2. Is it actually getting power at all? (off-peak systems)

If your system runs on a controlled load tariff, it only heats during set hours. A system that has been switched off, or a controlled-load meter fault, produces exactly the symptom of "no hot water" with nothing visibly broken. If the tank is stone cold in the afternoon and the breaker is on, this is worth raising with your electricity retailer before you assume the unit is dead.

3. Is the isolation valve open? (all types)

There is a valve on the cold inlet to the system. If work has been done recently — a new tap, a leak repair, a filter change — it can be left partly or fully closed. A closed inlet gives you no hot water while cold works fine everywhere.

4. Is the pilot out or has ignition failed? (gas)

This is the most common gas cause, and it is where this site stops. Older gas units have a standing pilot that can be blown out; newer ones have electronic ignition that can fail or lock out. We are not going to walk you through relighting it.

We do not give gas instructions, and neither should anyone else. In Australia, work on gas appliances is licensed gasfitting. A relight that goes wrong is not a leak you notice later — it is gas released into an enclosed space. If your gas unit has no flame, call a licensed gasfitter. If you can smell gas at any point, leave the area, do not operate switches, and ring your gas distributor's emergency line.

5. Has the unit locked out on an error? (heat pump and continuous flow)

Both types have controllers that display fault codes. Photograph the code before you do anything, including turning it off and on. That code is the single most useful thing you can hand a technician, and it very often distinguishes a cheap sensor fault from a dead compressor. Cycling the power sometimes clears a lockout — and if it comes straight back, the code is the real story.

6. Has the element or thermostat failed? (electric)

This is the most common electric cause and the most common reason people are told they need a whole new system. A tank with a failed element is otherwise fine. Symptoms: no hot water at all with the breaker holding, or hot water that lasts a few minutes then goes cold (upper element working, lower one dead).

Do not open the element cover. Behind it is mains voltage in a wet enclosure, and the element sits in a tank under pressure. Diagnosing it is a five-minute job for a licensed plumber or electrician with a multimeter. This is the diagnosis to ask for, not to attempt.

The question to ask before you agree to a replacement

If someone tells you the system needs replacing, ask which of these it is: a failed element or thermostat, a failed controller or sensor, or a leaking tank. The first two are parts. The third genuinely is the end of the system, because a corroded cylinder cannot be repaired.

Ask them to show you where it is leaking. A tank that is actually finished leaks from the cylinder itself, not from a valve or a fitting — see which leak is urgent, because the difference is the whole decision.

And if the system turns out to be old enough that a part replacement is only buying a year or two, that is a legitimate reason to replace — but it is a different conversation, and choosing the replacement deserves more than the ten minutes you have while standing in a cold shower.

Frequently asked questions

Can I reset the hot water breaker myself?

Resetting a tripped breaker once is reasonable. 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, and all three need a licensed trade.

Why do I get hot water for a few minutes and then it goes cold?

On an electric storage system that pattern usually means the lower element has failed. The upper element still heats the top of the tank, so you get a short burst of hot water and then the cold water underneath it. The tank itself is generally fine.

My gas hot water pilot light is out. Can I relight it?

We do not publish gas instructions. Gas appliance work in Australia is licensed gasfitting, and a failed relight releases gas into an enclosed space. Call a licensed gasfitter, and if you can smell gas, leave the area and ring your gas distributor's emergency number.

Is no hot water an emergency?

Not usually — it is uncomfortable rather than dangerous. The exceptions are a smell of gas, water pooling around an electrical unit, or scalding-hot water coming out of taps that used to be tempered, which suggests a failed tempering valve.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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