Tuesday night in Prestons. You go out to the garage and there's a wet patch spreading from under the hot water tank, and the little copper pipe on the side is dripping onto the slab. First question: is it going to burst? Almost certainly not. Second: do I need a plumber tonight? Usually not. Here's how to tell.
The short answer on a hot water system leaking: a small drip from the relief valve while the tank is heating is normal and by design. A steady stream from that valve, or water coming from the bottom of the tank itself, is not. The first is a valve or pressure problem and a repair job. The second usually means the tank has rusted through and it's replacement time. Neither is dangerous once you've switched off the power (or gas) and the cold water inlet, which I'll walk you through. If the shower is cold right now, we are a hot water plumber, no call-out fee, across Liverpool, Campbelltown and Camden.
A small drip from the relief valve while the tank heats is normal; a constant stream means a faulty valve or high mains pressure and is a business-hours repair. Water from the bottom of the tank means the cylinder has rusted through and needs replacing. Switch off the power or gas, close the cold water inlet, and it will safely hold until a licensed plumber gets there.
Where is the water actually coming from?
Dry the tank with a rag and watch it. The spot tells you most of what you need to know.
| Where it's leaking | Most likely cause | What to do |
|---|---|---|
| Copper pipe from the top or side, dripping only while heating | Temperature and pressure relief (TPR) valve doing its job | Normal, keep an eye on it |
| Same pipe, running constantly or more than a bucket a day | Faulty TPR valve, or mains pressure too high | Repair job, business hours |
| Small brass valve on the cold inlet dripping | Cold water expansion valve, normal in small amounts | Normal, repair if it runs constantly |
| Brass valve with a coloured cap on the hot outlet | Tempering valve seals or body failed | Repair job, check your tap temperatures |
| Around the element cover or thermostat panel (electric) | Element gasket perished | Switch the power off, repair job |
| From the bottom of the tank, or rust stains at the base | Cylinder corroded through | Isolate it, replace the system |
The hot water pressure relief valve: when a drip is normal
Every storage tank has a temperature and pressure relief valve, a brass valve near the top with a copper drain line running to the ground or a tundish. People call it the hot water pressure valve, the pressure relief valve or the TPR. Water expands as it heats, and in a sealed mains pressure tank that expansion has to go somewhere, so the valve lets a little out during each heating cycle. The manufacturers' owner's guides say a small discharge while heating is normal, and that more than a bucket in 24 hours means something is wrong.
When the relief valve isn't normal
If the drain line runs constantly, or you're seeing far more water than you used to, there are two usual suspects. Either grit is holding the valve seat open, or your mains pressure is higher than the valve is rated for and it's relieving all day. In parts of Liverpool and Cabramatta I see mains pressure well above what these valves like, and the fix is a pressure limiting valve on the inlet, not a new tank. Either way it's an hour's hot water system repair, not an emergency. Manufacturers also recommend replacing the relief valve every five years or so; a hot water heater pressure relief valve isn't built to last the life of the tank.
The easing lever, and the one thing never to do
The lever on top of the valve should be operated gently every six months: lift it, let a burst of hot water run down the drain line, lower it. That clears scale and proves the valve isn't stuck. Careful, the water is 60 degrees plus. What you must never do is cap, plug or crimp the drain line because the drip annoys you. That valve is the only thing standing between a thermostat fault and a tank that ruptures. I have found plugged relief lines in Fairfield, and I have removed them with the power off and a very straight face.
Hot water system leaking from the bottom
This is the one that matters. Most storage tanks are steel with a glass (vitreous enamel) lining, and a sacrificial anode inside that corrodes instead of the tank. Once the anode is used up, the steel goes next, and water eventually finds a pinhole or a seam at the base. There is no repair for a tank that has rusted through. If water is weeping from under the tank or the base of the cabinet is rusty and damp, the cylinder is finished.
It rarely goes from a weep to a flood overnight. Turn it off, isolate the water and it will hold until I get there in business hours. If you're wondering whether an older unit is worth more money, my post on how long hot water systems last covers the age check and the repair or replace rule of thumb.
Tempering valve leaking, and other odd spots
The tempering valve is the brass valve on the hot outlet that blends cold water in so your bathroom taps get 50 degrees rather than the 60 plus stored in the tank. That's an NSW requirement under the plumbing standard, and I explain it properly in tempering valves and thermostatic mixing valves. When one leaks it's usually the internal seals, or a body cracked by years of hot and cold cycling. If the leak comes with lukewarm showers or scalding ones, the valve is failing and it should be replaced, not tightened.
Flexi hoses and compression fittings on the inlet and outlet are the other regulars. A drip from a nut is often a quarter turn from fixed, but a hose with rusting or bulging braid gets replaced, because a burst flexi does more damage in a night than a leaking tank does in a month (ask anyone who's needed me for leaks and burst pipes).
What to switch off, and what to leave alone
If the tank body is leaking, or the relief valve is running hot and hard, do these in order.
- Electric: switch off the hot water circuit at the switchboard (usually labelled). Gas storage: turn the gas control knob on the unit to off, or close the gas isolation valve on the pipe into it. Leave the gas meter alone unless you smell gas.
- Close the cold water isolation valve on the inlet pipe to the tank. It's the tap or lever on the cold side, near the small brass expansion valve.
- Open a hot tap inside to take the pressure off. You'll still have cold water everywhere.
- Put a towel or a tray under the leak, and take a photo of the compliance plate (make, model, litres, date) to send me.
Don't lean on the fittings with a shifter (the brass is softer than you think), and don't drain the tank yourself unless you've been shown how; the water is hot enough to hurt.
What hot water system repairs cost in Sydney
For valve and fitting work, think of it as a call-out plus an hour or so. Sydney 2026 price guides put call-out fees at $69 to $170 and hourly rates at $92 to $230, most around $140. The part itself is quoted on inspection; a TPR valve, a tempering valve and a pressure limiting valve are all different prices. If the tank is gone, you're into replacement: the same guides put an electric storage system installed at $920 to $2,875 and gas storage at $1,375 to $4,025. What moves the number is access (a roof space or a tight cupboard takes longer), whether the old valves and pipework can be reused, and after-hours timing. A leak you've isolated can wait until morning, and I'll say so on the phone.
In NSW all of this is licensed work. The NSW Government is clear that any plumbing, draining or gasfitting work needs a licence regardless of cost. Swapping a valve on a pressurised tank of 60 degree water is not a tap washer.
When to call a plumber
Ring me straight away if hot water is pouring (not dripping) from the relief line and you can't isolate it, if the tank is leaking into a living space or onto electrical gear, or if you smell gas near a gas unit. Ring during business hours for everything else: a relief valve that won't stop, a tempering valve weeping, a weep at the base of a tank you've already isolated. If the problem is no hot water rather than a leak, start with what to check before you call; a tripped breaker costs nothing. Done right. Done once.
Monarch Civil & Plumbing covers South West Sydney and the Macarthur region for hot water system repairs and replacements, from Liverpool and Prestons out to Campbelltown, with 24/7 emergency call-outs when it can't wait. If you need a plumber in Prestons or anywhere nearby, call 0455 222 292 with a photo of the leak and I'll tell you what it is and what it'll cost before I come out.
Related guides: no hot water and how long hot water systems last.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a hot water plumber, no call-out fee: repairs where they are worth it, same-day replacement where we can, and the NSW rebate sorted.
No hot water in Campbelltown, Liverpool or Camden?
Campbelltown has its own page: hot water service Campbelltown. For Liverpool, Camden and the rest of South West Sydney start with hot water systems, then the suburb pages plumber Liverpool and plumber Camden. Same-day replacement for common electric and gas sizes where stock allows, no call-out fee, NSW rebate sorted for heat pumps.
Frequently asked
Is it normal for a hot water system to drip?
Yes, in small amounts. The temperature and pressure relief valve lets a little water out through its drain line as the tank heats, because hot water expands and needs somewhere to go. Manufacturers say a small discharge during heating is normal and that more than a bucket a day is not. A constant run means the valve or your mains pressure needs attention, and that's a business-hours repair rather than an emergency.
Can I replace the hot water pressure relief valve myself?
In NSW, no. Any plumbing work needs a licence regardless of cost, and a relief valve is a safety device on a pressurised tank of 60 degree water. What you can safely do is lift the easing lever gently every six months to check it isn't stuck. Replacing the valve is a short job for a licensed plumber and is priced as a call-out plus about an hour, with the valve quoted on inspection.
My hot water system is leaking from the bottom. Can it be repaired?
Almost never. A leak from the base or the bottom seam means the steel cylinder has corroded through, usually because the sacrificial anode was used up years ago. There is no lasting patch for that. Switch off the power or gas, close the cold water inlet, and plan a replacement. It will usually hold as a slow weep until business hours, so there is no need for a night call-out.
Should I turn the hot water system off if it's leaking?
If the leak is from the tank body or the element cover, or the relief valve is running hard and hot, yes. Switch off the hot water circuit at the switchboard (or turn the gas control to off on a gas unit), then close the cold water isolation valve on the inlet pipe. If it's a slow drip from the relief line while the tank heats, leave it on and just keep an eye on it.
Why is my tempering valve leaking?
Tempering valves have internal seals and a thermostatic element that wear out, and the body can crack after years of hot and cold cycling. A leak from the valve often comes with shower water that's too hot or only lukewarm. It needs replacing rather than tightening, and the new one must be set so bathroom fixtures get no more than 50 degrees, which is the NSW plumbing standard.
How much does a hot water system repair cost in Sydney?
Valve and fitting repairs are typically a call-out fee plus about an hour of labour. Sydney 2026 price guides put call-outs at $69 to $170 and hourly rates at $92 to $230, most around $140, with the part itself quoted on inspection. If the tank has failed, replacement runs $920 to $2,875 for electric storage and $1,375 to $4,025 for gas storage installed, depending on access and pipework.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul