A wet patch under a hot water unit is one of the most common emergency callouts we get on the Gold Coast. In almost every case where the water is coming from the body of the unit (not a fitting or connection), the diagnosis is tank failure and the answer is replacement.
What is actually happening inside the unit
Gas and electric storage hot water units have an inner steel tank inside an outer insulated jacket. The inner tank is protected by a sacrificial anode (a magnesium or aluminium rod that corrodes preferentially to protect the tank steel). When the anode is consumed (typically 5-10 years), the tank itself starts to corrode. Eventually a pinhole opens in the tank wall, water leaks into the insulation, and shortly after that, out of the bottom of the unit.
Once the tank wall is breached, there is no field repair. The tank is sealed, you cannot weld it from outside, and any patching is temporary at best. The unit needs replacement.
How to confirm it is the tank and not a fitting
- Trace the leak source. If water is coming from a visible pipe or fitting at the top of the unit, that is a fitting leak, often repairable for under $400. If water is coming from the body of the unit itself (especially the bottom rim), that is tank failure.
- Check the relief valve. Most hot water units have a pressure relief valve that drains a small amount during normal operation. If your leak is from a small pipe near the top of the unit running down to a drain, that may be normal valve operation, not tank failure.
- Check the connections. Inlet, outlet, gas (if gas unit) and electrical (if electric or heat pump). Wet fittings can sometimes be tightened or resealed.
If after these checks the water source is the body of the unit, it is tank failure.
What to do right now
- Turn off the water supply to the unit. Most units have an isolation valve on the cold water inlet. Turn it clockwise until firm. This stops the leak.
- Turn off the gas (gas units) or electricity (electric / heat pump units) to the unit. Gas isolation valve usually nearby, electrical isolation at the unit's switch or the breaker.
- Drain the tank if it is leaking heavily. Open a hot tap somewhere in the house to release stored hot water faster.
- Mop or vacuum any standing water to limit damage.
- Call us on 0472 657 042 to arrange a replacement. Same-day replacement is usually possible for common units (gas storage, gas continuous flow, common electric storage). Heat pumps and premium units may be next-day.
Will insurance cover the water damage?
Most Australian household insurance policies cover water damage from sudden hot water unit failure, but they often exclude damage from a leak that has been going on slowly for a long time. The faster you isolate and call, the cleaner the claim. We provide an itemised invoice with cause-of-loss documentation that almost every Australian insurer accepts.
Could the anode have been replaced to prevent this?
Yes, usually. Sacrificial anodes have a 5-10 year service life. If you replace the anode at year 5 and again at year 10 ($250-400 each time), the tank itself can last 16-22 years instead of 8-12. Most owners never replace the anode and lose half the potential tank life as a result. We track every unit we install and message owners when anode service is due.
What should I replace with?
Almost certainly not the same gas storage or electric storage unit. The economics now favour either heat pump (lower running cost, federal STC rebate) or gas continuous flow (endless hot water for higher-demand households). We will quote 2-3 options at quote stage with realistic 10-15 year cost projections so you can compare total cost. See our heat pump and hot water system pages for the full conversation.
If your leak is from a continuous flow unit instead of storage
Gas continuous flow units do not have an inner tank, so the failure mode is different. A leak from a continuous flow unit is almost always a connection or internal component failure, sometimes repairable. We will diagnose at the door, $200-680 for most repairs, replacement only if the heat exchanger has failed (which is the end-of-life condition for these units).
Reading the puddle, what the water tells us before we even open the unit
The pattern of water under a hot water unit tells us a lot before we touch anything. A wide even puddle directly under the centre of the tank means the tank has rusted through near the base, classic anode-neglect failure on a 9-14 year old gas or electric storage unit. A puddle to one side with rust staining tells us the corrosion is offset, sometimes from a manufacturing weld defect or from water pooling against one side of the casing due to an out-of-level install. A small recurring wet spot near the relief valve overflow with no rust is usually normal valve discharge during heating cycles, not a failure. Water running down a wall from the top of the unit is a fitting or inlet leak, often a $200-400 repair rather than replacement. Water around the gas valve assembly on a continuous flow Rinnai or Rheem points to internal heat exchanger failure or a cracked solenoid housing, repair or replacement decision depends on age. Water with a metallic taste or rust colour confirms the leak is from inside the tank rather than from a fitting carrying clean potable water. We diagnose at the door, then quote.
The hidden water damage timeline most homeowners miss
A slow tank leak does not announce itself. The first wet patch a homeowner notices is usually weeks or months after the tank started weeping into the insulation jacket. By the time water shows on the floor, the insulation is saturated, the casing base is rusting from inside, and adjacent surfaces are quietly absorbing moisture. We have pulled units out of Robina laundries where the underlying floor timbers were rotted, units from Tallai sub-floor installs where the bearers needed replacement, and units from Coomera garages where the gyprock wall behind the unit was black with mould. The repair scope expands fast once you peel back what the slow leak has been doing. Catch it within the first week and the damage stops at the unit itself. Wait a month and you can be into $2,000-5,000 of additional plumbing, carpentry and mould remediation on top of the replacement HWU. The lesson, act the same day you spot moisture, not the following weekend. If you cannot get a plumber to attend immediately, at minimum isolate the cold water supply at the unit isolation valve and turn off the gas or electricity, that stops the leak from growing while you wait.
What happens when the relief valve is the actual culprit
Not every wet patch under a unit is tank failure. Pressure and temperature relief valves (PTR valves) are designed to discharge water if the tank over-pressures or over-heats, that discharge runs down the overflow pipe to a drain or external grate. A failed PTR valve drips constantly even when the system is operating normally, sometimes mistaken for tank failure. The fix is a new PTR valve, $180-320 supplied and installed. We diagnose by checking valve discharge temperature, valve seat integrity, and tank pressure, none of which a homeowner can easily do. If a previous plumber has capped or blocked an overflow pipe (we still see this on older Surfers and Broadbeach units), the valve has nowhere to vent and water finds its way out around the base of the unit instead, looking exactly like tank failure. Always check the overflow line is clear and unblocked. A blocked overflow combined with a stuck-open PTR valve is the most common false-alarm replacement we are called to inspect, sometimes catching the issue before the homeowner has committed to a $3,000 replacement they did not need.
Replacement-day logistics, what actually happens at your house
Same-day replacement is achievable for the common units but requires sequencing. We arrive with the new unit on the van (Rinnai Infinity 26, Vulcan Freeloader 170L, Rheem 250L electric, Sanden 250L heat pump are the common in-van stock). Step one, isolate water, gas and electricity. Step two, drain the old tank, takes 20-40 minutes via the relief valve overflow or a garden hose tail on the drain cock. Step three, disconnect old unit, remove via two-person lift or trolley depending on location. Step four, prep the install location, check the wall plate, replace any old galvanised pipe tails with copper, fit new isolation valves. Step five, mount the new unit, run tails, connect gas (with manometer leak test) or electrical (with insulation resistance test). Step six, fill the tank, bleed air, commission. Step seven, walk-through with the homeowner, explain temperature setting, show the isolation valves, hand over the compliance certificate and warranty card. Total time on site, 3-5 hours typical for storage units, 2-4 hours for continuous flow, 4-6 hours for heat pump including electrician sub. You are back on hot water the same day in most cases.
The insurance claim documentation we provide and why it matters
Australian household insurance covers sudden hot water unit failure on most standard policies, but the documentation requirements vary by insurer. Allianz, NRMA, AAMI, Suncorp and Budget Direct all require, at minimum, an invoice showing the date and cause of failure, the licence number of the plumber, the brand and age of the failed unit, and confirmation that any consequential water damage was a direct result of the failure rather than a pre-existing slow leak. We provide all of this on every emergency callout invoice as standard. Where useful, we also photograph the failed unit before removal showing the leak source, the rust pattern on the tank, and the surrounding water damage, all timestamped. Claims that include this documentation routinely settle within 5-10 business days. Claims without it get bounced back by the insurer for more information and the average settlement timeline doubles. If your unit has failed and you intend to claim, ask your plumber at booking whether they provide cause-of-loss documentation. We do, every time, no extra charge.
The temporary patch options that buy you 24-48 hours, no more
If your hot water unit has just started leaking and you cannot get a replacement until tomorrow or the day after (peak demand periods, public holidays, supply shortages on a specific brand), there are short-term measures that buy you time without making the eventual replacement any harder. Isolating the cold water supply at the unit stops the active leak completely, you lose hot water but you stop water damage. Reducing tank pressure by opening a hot tap somewhere in the house drains residual hot water into use and reduces the head pressure on the leak point. Placing absorbent material (old towels, a few microfibre cloths) around the base of the unit catches drips and prevents floor staining and adjacent timber rot. Running a small fan in the room maintains airflow that reduces mould risk on adjacent gyprock and skirting. What you should not do, no patching attempts on the tank itself, no epoxy or sealant on the leak point (we have seen DIY patches make the tank impossible to safely drain, complicating replacement and adding labour time), and no continuing to use the unit for showers (the leak gets worse the more the unit cycles). The short-term measures keep the situation contained for 24-48 hours while you arrange proper replacement. Beyond 48 hours the damage to adjacent surfaces starts to compound.