Hot water system leaking or burst: what happens next

A hot water system failure is a burst pipe with two differences: the volume arrives all at once, and the failure was predictable. The first is an engineering problem and the second is an insurance one.

If it is leaking now

1. Close the cold water inlet valve at the top of the unit. This is the one that stops it refilling. Everything else is secondary.
2. Kill the power or the gas. Electric: the dedicated circuit at the switchboard. An element energised in a draining tank will burn out and can be a fire risk. Gas: the control knob to off or pilot.
3. Open a hot tap somewhere in the house to relieve pressure and let the tank drain in a controlled way rather than through the failure.
4. Photograph it before it is moved. The unit, the compliance plate with the date on it, the failure point, the water line on the wall, the extent of the spread. Plumbers take failed units away, and once it is gone the evidence is gone.

Where the water goes

Australian domestic storage units are commonly between 125 and 400 litres. The tank contents are the beginning, not the total: once the tank has a hole in it the inlet keeps feeding it at mains pressure until someone closes the valve, so an overnight failure puts far more than a tank’s worth on the floor.

Where they are installed determines what gets wet:

• Internal laundry or cupboard. The worst case. Water goes into adjoining rooms through the wall plate and under the skirtings, and it travels along joists in a suspended floor, which is why the damp patch appears in a room that does not adjoin the laundry.
• Garage. Usually a graded slab and a drain. Often the cheapest version, unless it runs under an internal wall.
• External wall. Best case for the building, but check the subfloor and the wall base, because external units discharge against the wall they are mounted on.
• Roof space (rare but real). Worst case of all. The ceiling comes down and the entire room below is affected at once.

Why this is the hardest wear-and-tear case

With a flexible hose, the insurer has to reason about a component with no documented service life. With a hot water unit it does not have to reason at all: manufacturers state expected service lives, warranties are written against them, and a corroded cylinder at the end of a documented life is the textbook example of the thing reg 19(2)(b) excludes.

So the expected outcome is clean and it is worth knowing in advance: the water damage is a listed event and is typically paid; the unit is not and is typically declined. Budget for a new unit, and do not treat the decline of the unit as a decline of the claim.

The one place this gets interesting is a young unit that failed. A four-year-old cylinder that corroded through is not wear and tear in any ordinary sense, it is a defective product, and that is a warranty conversation with the manufacturer rather than an insurance one. Keep the unit if you can.

The two invoices

hipages publishes Australian plumber rates of $80 to $200 per hour with call-out fees of $150 to $250, in a guide last updated 24 July 2026. A replacement unit is on top of that and this site does not publish a figure for it, because no unit price was read from a primary source.

The drying is the other invoice. A laundry plus the adjoining room, dried over the published minimum hire of 3 days, comes to $1,557 excluding GST on the rate card this site reproduces. Five days, which is more realistic where water has gone under a wall into a second room, is $2,269.

The part that gets missed

Hot water failures produce a characteristic pattern of hidden damage, because the water is hot and hot water moves differently:

• Wall bases. Plasterboard wicks upward. The visible mark is lower than the actual moisture line, sometimes by 200mm.
• Under vinyl and laminate. Both are effectively vapour barriers. Water underneath them does not evaporate and does not show, and laminate substrate swells irreversibly.
• Subfloor cavities. In a suspended timber floor the water goes down and then sideways. This is what moisture meters and thermal imaging are for, and it is the reason a restorer’s assessment is worth more than a look around.
• Insulation in the wall. Wet bulk insulation does not dry in place and does not recover its R-value. It has to come out, which means opening the wall.

Ask for the moisture map. A restoration company that has taken readings has a document showing where the water is, and that document is what stops the scope being argued about later.

Common questions