Water under a hot water system means one of about four things, and only one of them is a dead tank. The gap between "that is the safety valve doing its job" and "you need a new unit by Friday" is usually visible in five minutes, once you know where to look. Most people skip those five minutes and assume the worst, which is how perfectly good tanks get replaced.
Here is how a plumber works it out. If water is running rather than dripping, or it is near electrics, stop reading and call the emergency plumbers in Parramatta now.
A relief valve that discharges into its drain line while the tank is heating is the system working as designed, not a fault. Water weeping from the base of the cylinder, rust stained and constant, is the tank, and that one never gets better. Turn the power or gas off, close the isolation valve on the cold inlet, dry everything, and watch where the water comes back from.
- Switch the power or gas off at the unit
- Close the isolation valve on the cold water inlet
- Dry the area completely and put paper down
- Wait twenty minutes and find where the water restarts
- Check the relief valve drain line before you assume the worst
- Photograph it, then call a licensed plumber
On this page
1. Power or gas off, then close the cold inlet
Take the heat out of it first. On an electric unit, switch off its circuit at the meter board or the isolation switch beside it. Hot water usually sits on its own circuit, so this will not black out the house. On gas, turn the gas control to off. An element sitting energised in a tank that is quietly emptying burns itself out in minutes, turning a leaking valve into a leaking valve plus a dead element.
Then close the isolation valve on the cold inlet, the small lever on the pipe entering the top of the unit. It turns a quarter turn to sit across the pipe. In a freestanding home, if there is none, fall back to the main tap at the front boundary, which our burst pipe guide covers in detail. In an apartment there is no front boundary tap to fall back on, so the valve in the hot water cupboard or the riser is the only thing that will stop it, and that is most homes around here.
Unless a plumber has told you to on the phone, leave it full. Draining a storage cylinder yourself is how people end up with a scalding hazard, or 250 litres of hot water somewhere far less convenient than where it already was.
2. Follow the water back to its source
Water tracks. It runs along the base, down the wall, across a slab and surfaces somewhere that looks nothing like where it started. Almost every wrong diagnosis begins with a puddle at the front of the unit and the assumption that the front of the unit is where it came from.
Dry everything, including the top of the unit and the pipework, then lay paper towel around the base and under the drain line outlet. Give it twenty minutes with the power off. The first wet paper tells you more than an hour of guessing. There are four realistic candidates:
- The temperature and pressure relief valve, discharging through its drain line. Usually the good news.
- A valve or fitting on top of the unit. A cheap part, not a new system.
- The cylinder itself, weeping from the base. The end of the road.
- Something that is not the unit at all. Much of Parramatta sits on Wianamatta shale, a reactive clay that swells wet and shrinks dry and works buried pipe joints apart. If the unit is bone dry and the ground around it is not, you are looking at the cold line, which is a different job.
3. Is it the relief valve? Usually, and that is the good outcome
Every mains pressure storage heater has a temperature and pressure relief valve. Its job is to let water out if pressure or temperature climbs past a safe point, which is the difference between a hot water system and a bomb. A drain line runs from it to a visible spot outside.
Water expands when heated and is not compressible, so the extra volume has to go somewhere. Without a working expansion control valve, it goes out through the relief valve. So some discharge during the heating cycle is completely normal. What is not normal is a constant run, or hot water from the drain line all day. That points at grit holding the valve seat open, a failed expansion control valve, or supply pressure high enough that the valve sits close to lifting all the time. All three are ordinary repairs.
Where the line discharges matters too. The NSW plumbing advisory is explicit that relief valve and expansion control valve drain lines must not discharge into a safe tray, and that the discharge point must be placed so a release of steam or hot water "does not cause a nuisance, is readily discernible and incurs no risk of damage to the building or injury to persons". Readily discernible is the key phrase. The valve is meant to tell you when it operates, and plenty of installs we see have buried that line where nobody will notice it.
Relief valves are also consumable. Rheem's service schedule for its electric heaters replaces the relief valve as part of a major service every five years. If nobody has touched yours in a decade, a weep is not a surprise, it is a maintenance item that came due.
Capping, wedging or over-tightening a relief valve to stop a drip removes the only thing standing between a pressure vessel and a failure. If it discharges constantly it gets replaced, not silenced, and in NSW that is not a job for anyone unlicensed.
4. Is it a valve or fitting on top?
If the water starts at the top rather than the bottom, look at the brass. Stored water sits at 60 degrees or more to keep legionella down, while water delivered to a bathroom or hand basin outlet is capped at 50 degrees, and the thing bridging that gap is a tempering valve.
Tempering valves fail, and so do the unions either side of them, the isolation valves, the expansion control valve and the flexible connections. Any of those weeping at the top runs down the outside of the cylinder and pools at the base, which from a metre away looks exactly like a dead tank. It is the most common reason a healthy system gets condemned.
The tell is the staining. Water from a valve or union is clear and the trail starts above the base. Water from a failed cylinder is rust marked and starts at the bottom seam, with nothing wet above it.
Not sure which one you have?
Send a photo or just describe it. If it is a valve we will tell you, and if it is the tank we will tell you that too.
5. Is it the cylinder itself?
This is the one people search for as a leak from the bottom, and the answer is short. A storage cylinder is glass lined steel. Inside sits a sacrificial anode, a rod whose whole purpose is to corrode instead of the tank. Once it is spent the steel gives way instead, from the inside, where nobody can see it. When it perforates you get a weep at the base that grows, and a perforated cylinder cannot be repaired. No patch, weld or sealant safely holds mains pressure on a corroded pressure vessel. The unit gets changed over.
The signs, most conclusive first: rust coloured water rather than clear, a leak at the base seam with dry pipework above it, a rate that worsens rather than holding steady, and rusty hot water at the taps in the weeks beforehand. Two or more together and you are almost certainly looking at a replacement.
Before you accept that, the anode decides when this happens and it is replaceable. On the soft Prospect supply that feeds Parramatta the anode is the clock on the tank, not scale, and Rheem's guidance is that on softened or desalinated supplies it should be inspected within five years of installation, with eight years the outside limit across all supplies. Swapping one on a tank that is otherwise sound costs a fraction of a new system and buys years. Almost nobody does it, which is why so many units here die younger than they need to.
6. If your tank is on controlled load, the timing tells you a lot
This is the test that works in Parramatta and does not travel, so it is worth being precise. Parramatta sits in the Endeavour Energy network, not Ausgrid. On Endeavour's Controlled Load 1 tariff, supply to the heater "may not be available between 7:00am and 10:00pm", and "supply will be made available for selected periods between 10:00pm and 7:00am". That is their 2025-26 network price list, effective 1 July 2025.
Follow that through. If your tank is on controlled load the element only fires overnight, so the water only expands overnight, so a thermal expansion discharge happens overnight too. The pattern is a wet patch under the drain line at 6am and a bone dry line by lunchtime. That gives you a useful diagnostic:
- Wet in the morning, dry by afternoon, clear water, from the drain line. That is the heat cycle. Worth checking, but not an emergency and not the tank.
- Same rate all day and all night. Not the heat cycle. A valve holding open, a fitting, or the cylinder.
- Worse right after someone showers. Points at the inlet side or the tempering valve, because that is when cold water is moving into the unit.
Why this is a Parramatta answer rather than general Sydney advice: in Ausgrid suburbs, Controlled Load 1 is supply "usually connected for at least six hours duration within any 24 hour period: midnight to midnight", and Ausgrid moved those switching times in July 2024 specifically to use daytime solar. An Ausgrid tank can be heating mid-afternoon. Run the overnight test in Bondi or Chatswood and it tells you nothing.
One thing to settle before replacing anything on this tariff: Endeavour allows a heat pump on Controlled Load 2 with a minimum tank size of 250 litres, but states that pump "cannot be consequently transferred to the Controlled Load 1 Pricing Option". Get the tariff question answered before the unit is ordered, not after.
7. In an apartment, the safe tray is the thing that matters
About 85.6 per cent of Parramatta's occupied private dwellings are flats or apartments, against 7.7 per cent separate houses, so for most people reading this the hot water system is in an internal cupboard, not out the back. That changes the problem completely, because the floor under your unit is somebody else's ceiling.
A storage heater installed inside a building, in a cupboard or a roof space, has to sit in a metal safe tray draining to a visible point. The tray is not decoration. It catches a failing cylinder and sends the water somewhere harmless instead of through the slab. So the first question in an apartment is not "is it the tank", it is "is the tray working". Water on the cupboard floor rather than out of the tray's drain means the outlet is blocked, or the leak is above the tray. Either way it is heading for the unit below, and the damage down there will cost more than the hot water system ever will.
Who pays depends on where the leak starts, not where the damage appears. Water starting in common property is the owners corporation's; water starting inside your lot is yours. The complication is the common property memorandum under the Strata Schemes Management Act 2015, which only applies where a scheme has adopted it, and which can shift responsibility for a hot water unit onto the lot owner. Ask your strata manager which applies before you assume, and tell the building manager the moment you find water. In a Parramatta CBD or Westmead tower that call is more urgent than the plumbing one.
8. Why Parramatta hot water systems fail the way they do
Three local realities decide how long a tank lasts here, and none of them is the one the internet will tell you.
The water is soft, so forget limescale. Supply to Parramatta from the Prospect system runs at roughly 50 mg/L hardness, inside the soft range below 60 mg/L. Every generic article blaming hard water and scale for tank failure is describing somewhere else. Here the failure is corrosion, which comes down to the anode and the steel. Soft water does not spare the anode either, which is why manufacturers shorten the inspection interval on soft and softened supplies rather than extend it.
Supply pressure varies street to street. Sydney Water states that most properties receive between 15 and 65 metres head, that the network average is 52 metres, and that properties in low areas receive higher pressure while properties in high areas receive lower. Parramatta covers a lot of ground vertically, from the river flats around the CBD, Harris Park and Rydalmere up to the ridges at Northmead and Winston Hills, so two homes a few streets apart genuinely sit at different pressures. Higher pressure means a relief valve closer to its lifting point and harder work for every seal in the house, which is why an expansion control valve and a pressure limiting valve earn their keep on the low side of the suburb.
The pipework is often older than the unit. Plenty of homes in Harris Park, North Parramatta and Granville still run original galvanised pipework, which corrodes from the inside and narrows as it goes. Sydney Water's own pressure advice notes corroded galvanised pipes may not perform well when supply pressure is reduced. A new tank fed by tired galvanised is a new tank with an old problem.
9. Five things that make it worse
- Plugging or over-tightening the relief valve. The most dangerous thing on this list. It stops the drip by removing the safety device.
- Turning the thermostat up to compensate. More stored heat means more expansion, more discharge, and a scalding risk if the tempering valve is also struggling.
- Leaving the power on. An element in a draining tank cooks itself. Two minutes at the switchboard saves a part.
- Bucket under it, deal with it later. A corroding cylinder does not stabilise. Weeps become splits, and they rarely choose a weekday.
- Assuming the safe tray has you covered. A tray with a blocked outlet is a shallow bathtub in a cupboard, and in a suburb where five dwellings in six are apartments that bathtub is sitting on someone's ceiling. Check the drain runs before you rely on it.
10. When it is an emergency, and when it can wait
Call straight away, at any hour, if water is near electrics or the switchboard, if you cannot stop the flow with the isolation valve or the main tap, if the unit is rumbling or discharging steam or boiling water, or if you are in an apartment and water is heading for the unit below.
It can genuinely wait if the discharge is a cyclic drip from the relief valve drain line, the water is clear, the line runs to a proper outside discharge point, and there is no rust staining. Turn the power off to stop it entirely and book the next available appointment. That is a valve problem and an ordinary daytime job, and we would rather tell you so on the phone than charge an after hours rate to say it in person.
Whichever it is, it is licensed work. Unlicensed plumbing in NSW can void your insurance, and on a mains pressure system the licence is doing real safety work. Ours is 368473C and it goes on every quote. Our hot water repairs and replacement page covers the job, and our leaks and burst pipes page is the right start if the water turns out not to be the unit at all.
- Power or gas off, cold inlet closed, dry everything, then watch where the water restarts.
- A cyclic drip from the relief valve drain line while the tank heats is normal. Constant discharge is not.
- On an Endeavour controlled load tank the element only fires between 10pm and 7am, so wet in the morning and dry by lunchtime points at the heat cycle, not a fault.
- Clear water starting above the base is a valve. Rust stained water at the base with dry pipework above it is the cylinder, and that is a replacement.
- Parramatta's water is soft, so tanks here die of a spent anode and corrosion, never limescale. In an apartment, check the safe tray drain first and tell the building manager.
Leaking hot water FAQs
Why does my hot water system only leak overnight?
Parramatta is in the Endeavour Energy network, and on the Controlled Load 1 tariff supply to the heater may not be available between 7:00am and 10:00pm, with supply made available for selected periods between 10:00pm and 7:00am. So the element only fires overnight, and the water in the tank only expands overnight. A small discharge from the relief valve drain line during that heating cycle is the system working as designed, which is why you find a wet patch at 6am and a bone dry drain line by lunchtime. A leak that runs at the same rate all day is not the heat cycle.
Is my hot water system leaking because of hard water or limescale?
No. Water supplied to Parramatta from the Prospect system is soft, roughly 50 mg/L, well under the 60 mg/L mark where water starts being called moderately hard, so limescale is not what kills tanks here. What ends a storage cylinder in Parramatta is the sacrificial anode running out and the steel corroding from the inside. Soft water does not protect the anode, and manufacturers shorten the inspection interval on soft and softened supplies rather than lengthen it.
There is water in the hot water cupboard of my Parramatta apartment. Who pays?
Around 85.6 per cent of Parramatta's occupied private dwellings are flats or apartments, so this is the common version of the problem here. A storage heater installed inside a building sits in a metal safe tray draining to a visible point, so water on the cupboard floor usually means the tray outlet is blocked or the leak is above the tray. Who pays depends on where the leak starts, not where the damage shows. Tell your strata manager straight away and ask whether your scheme has adopted the common property memorandum, because that document can move responsibility for a hot water unit onto the lot owner.
Can a leaking hot water tank be repaired?
If the leak is a relief valve, a tempering valve, an expansion control valve, a union or an element seal, yes, and those are cheap parts rather than a new system. If the cylinder itself has perforated and water is weeping from the base with rust staining, no. It is a glass lined steel pressure vessel, and no patch, weld or sealant safely holds mains pressure once the steel has gone.
My neighbour's hot water system lasted twice as long as mine. Why?
Two reasons, and both are local. Sydney Water supplies most properties at between 15 and 65 metres head, averaging 52 metres, and states that properties in low areas receive higher pressure while properties in high areas receive lower. Parramatta runs from the river flats around the CBD, Harris Park and Rydalmere up to the ridges at Northmead and Winston Hills, so two homes a few streets apart genuinely sit at different pressures. The other reason is servicing: an anode that gets replaced buys years, and almost nobody replaces one.