Hot water system leaking: where it drips decides everything
A hot water system that leaks is not automatically a hot water system that needs replacing. Where the water is coming from tells you whether this is a valve, a fitting or the end of the tank.
Find the source before you accept a diagnosis. Stand where you can see the whole unit, dry everything with a towel, and come back in an hour. Water tracks along pipes and down casings, so the puddle on the ground is often nowhere near the leak.
1. Dripping from the relief valve pipe
Storage systems have a temperature and pressure relief valve — the TPR valve — with a discharge pipe running to a safe point outside. Some discharge from this pipe is normal and expected. Water expands when it is heated, and that expansion has to go somewhere; on a heating cycle a healthy system releases a small amount.
What is not normal is continuous discharge, or a sudden increase in how much comes out. That usually means one of three things: mains pressure at the property is too high and there is no working pressure limiting valve, the valve itself has partially failed or has debris on the seat, or the thermostat is letting the tank overheat.
That last one matters. The TPR valve is the safety device that stops a storage cylinder from becoming a pressure vessel. A valve venting hard is doing exactly what it was fitted to do, and the correct response is to find out why — never to cap, plug or restrict the discharge pipe.
2. Water at a fitting or union
Look at the connections on top of, or into, the unit: cold inlet, hot outlet, the relief valves, and on gas units the water connections. A weep at a threaded joint or union is a fitting problem, not a tank problem. These are repairable and have nothing to do with the age of the cylinder.
Same for the tempering valve and any isolation valve on the assembly: they are serviceable parts sitting outside the tank.
3. Water pooling at the base of the unit
This is the ambiguous one, and it is where the diagnosis actually gets made. Water at the base can be a fitting above it that has been dripping down the casing all along — or it can be the cylinder itself, corroded through, with water escaping inside the outer jacket and finding its way out at the bottom.
The way to tell them apart is patience, not opinion. Dry everything thoroughly, including up inside the casing as far as you can reach, then watch. If water reappears at a joint first, you have a fitting. If the unit stays dry everywhere you can see and water still appears at the base, the leak is inside the jacket.
4. Rust-coloured water, or water from the jacket itself
If the water is discoloured, or you can see rust staining on the outside of the casing where water has been running, that is the cylinder. A corroded storage cylinder cannot be repaired. There is no patch, no sealant and no internal coating that is a real fix; the tank is a pressure vessel that has lost its integrity, and the only answer is replacement.
This is also the moment where the sacrificial anode stops being an abstract idea. A cylinder that has corroded through has usually spent years with a fully consumed anode, and the anode is the part that was supposed to be replaced before this happened.
What to do right now
- If water is coming out fast, close the cold inlet isolation valve on the system. If you cannot find it or it will not turn, use the main stop tap at the meter. This stops the tank refilling as it empties.
- If the unit is electric, switch off its circuit at the switchboard as well. A leaking tank and a live element are a combination to remove, not to manage.
- If it is gas, do not attempt to isolate anything on the gas side yourself — turn off the water and call a licensed gasfitter.
- Do not turn the temperature down as a workaround. If the leak is a TPR valve responding to overheating, lowering the thermostat can mask a fault that is still there.
Repair or replace: the honest split
A leak at a valve or a fitting is a repair, regardless of the system's age. A leak from the cylinder is a replacement, regardless of how new it is — and if it is genuinely new, that is a warranty conversation, so find the paperwork before you agree to anything.
The failure mode to watch for is being told a tank is finished when nobody has actually dried the unit and watched it. Ask the person quoting you to show you where the water is coming from. If they can point at the cylinder, they are right. If the answer is vague, get a second look before you spend on a whole system — and then choose the replacement properly.
Frequently asked questions
Is it normal for water to drip from the hot water relief valve?
A small discharge during a heating cycle is normal — heated water expands and the valve releases the expansion. Continuous discharge is not normal and usually points to high mains pressure, a failed valve, or a thermostat letting the tank overheat.
Can a leaking hot water tank be repaired?
If the leak is at a valve, a union or a fitting, yes. If the cylinder itself has corroded through, no — there is no sealant or patch that is a genuine repair on a pressure vessel, and it has to be replaced.
Should I turn the water off if my hot water system is leaking?
If it is leaking more than a drip, yes: close the cold inlet isolation valve on the unit, or the main stop tap at the meter. On an electric system, switch off its circuit at the switchboard as well.
Why is my hot water rusty?
Discoloured hot water often means corrosion inside the cylinder, which usually means the sacrificial anode was consumed some time ago. It can also follow mains work that has disturbed sediment, so check whether cold water is affected too.
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.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- NSW Fair Trading. Plumbers, drainers and gasfitters — licensing