A leaking hot water system is one of those problems that looks the same whether it’s trivial or terminal. A puddle under the unit could mean a $30 valve, or it could mean the tank has rusted through and no repair will save it. The location of the leak is what separates the two.

Where is it actually leaking from?

Before anything else, work out the source. Water travels — it runs down the outside of the tank and pools at the base, so a puddle on the floor tells you almost nothing on its own. Dry the unit completely, then watch where the first new water appears.

1The relief valve is dripping

The temperature and pressure relief (TPR) valve is the small valve on the upper side of the tank with a copper pipe running down to the ground. Some discharge here is completely normal — water expands as it heats, and the valve releases that pressure. A cup or two a day is expected. A constant stream, or a sudden increase, is not: it usually means the valve has failed or your mains pressure is too high. This is a cheap, routine replacement, and relief valves are generally due every five years regardless.

2The inlet or outlet connections are wet

The cold water inlet and hot water outlet at the top of the unit are threaded connections that can loosen or corrode. Usually the cheapest repair on this list. Often it’s just a fitting that needs resealing. Worth catching early, because water running down the tank exterior accelerates rust on the casing.

3The tempering valve is leaking

The tempering valve mixes hot and cold so water reaches your tapware at a safe temperature — it’s what keeps outlet temperature at or below 50°C, which is a legal requirement for bathrooms and other personal hygiene outlets. These have a service life of around five years. A leaking one is a straightforward replacement, but don’t ignore it: a failing tempering valve can also cause scalding-temperature water at the tap.

4The drain valve is dripping

The tap-like valve at the base, used to empty the tank for servicing. Often just needs tightening or a new washer. Sometimes sediment stops it seating properly after a service. Minor, but it won’t stop on its own.

5Water is coming from the tank itself

If water is seeping from the body or the base seam of the tank rather than from a valve or fitting, the tank has corroded through and the system needs replacing. There is no repair for this. Steel tanks are protected internally by a sacrificial anode, and once that’s spent, the tank rusts from the inside out. This is the one leak that is always terminal.

How old is the system?

Age changes the maths. Most storage systems last between eight and twelve years, and there’s a full breakdown in our guide to how long hot water systems last. Spending money on a repairable fault in a nine-year-old tank often means paying twice within eighteen months.

System age	Leaking valve or fitting	Leaking tank
Under 5 years	Repair — likely still under warranty	Replace, and check warranty first
5–10 years	Repair	Replace
Over 10 years	Repair only if the system is otherwise sound	Replace

If you’re heading for a replacement, our guide to what it costs to install a hot water system covers what actually drives the final figure.

Why this matters more in Canberra

Canberra sits colder than any other major Australian city, with overnight temperatures below zero through much of June to August. That matters for leaks in two ways.

First, a system already struggling will usually fail in winter, when it’s working hardest and you can least afford to lose it. A small leak noticed in autumn is a scheduled repair. The same leak ignored becomes a cold shower on a frosty morning.

Second, exposed pipework and relief valve discharge lines can freeze. Ice in a discharge line blocks the valve’s ability to relieve pressure, which is exactly what that valve exists to prevent. If you have an outdoor unit and you’re seeing unusual discharge behaviour after a cold snap, get it looked at rather than waiting.

What you can check yourself

None of this requires tools, and all of it helps whoever you call.

Dry everything and wait

Towel the unit down completely, including under the base. Come back in an hour and note exactly where the first water appears. This single step is the difference between a diagnosis and a guess.

Check the relief valve discharge pipe

Find where the copper pipe from the relief valve terminates, usually near ground level. Is it dripping occasionally, or running continuously? Occasional is normal. Continuous is not.

Find the compliance plate

There’s a plate or sticker on the unit with the manufacturer, model and date. Photograph it. It tells a plumber the system’s age, capacity and whether parts are still available — and it’s the fastest way to get an accurate quote over the phone.

Note whether hot water still works

A leak with normal hot water is a different problem to a leak with no hot water. Mention both.

What not to do

Don’t tighten the relief valve or plug the discharge pipe to stop the dripping. That valve is a safety device — it’s the only thing preventing pressure build-up in a sealed vessel full of water at 60°C, and blocking it is genuinely dangerous.

Don’t attempt any work on a gas unit yourself. Gas hot water work requires a licensed gas fitter by law, and it isn’t a grey area.

Don’t leave an electric system powered on if the tank is draining. Elements that fire without water in contact will burn out, turning a repairable leak into a bigger bill.

Common questions

Is a leaking hot water system an emergency?

A dripping valve isn’t — book it in normal hours. Water running continuously, pooling against the house, or entering a wall or subfloor is, because water damage compounds by the hour. Complete failure with no hot water in the middle of a Canberra winter is worth treating as urgent too.

Can a leaking hot water tank be repaired?

Not the tank itself. Valves, fittings and connections are all repairable; a corroded tank is not. Anyone offering to patch or weld a leaking tank is selling you a short and unreliable reprieve.

Why is my relief valve dripping?

Some discharge is normal thermal expansion. Constant discharge usually means a failed valve or excessive mains pressure. Both are fixable, and neither should be ignored, because the valve is doing safety work.

How much water will a failed tank release?

Whatever the tank holds, commonly 125 to 315 litres, plus continuous mains flow until the supply is isolated. This is why knowing where your isolation valve is matters before anything goes wrong.

Will my insurance cover it?

Policies commonly cover resulting water damage while excluding the failed appliance itself, but this varies by insurer and policy. Photograph everything before any work starts, and check your product disclosure statement.

Does a leak mean I need a whole new system?

Only if the leak is from the tank. Four of the five common leak points are repairable parts. Get the source identified before assuming the worst.

If the system has stopped producing hot water altogether as well as leaking, that points to a different fault — see our hot water systems page for repair and replacement options, or call for same-day assessment.