The short answer
Where a hot water system is leaking tells you the next step. A small drip from the temperature/pressure relief (TPR) valve drain while the unit is heating is common on mains-pressure storage tanks. A constant flow from that pipe usually means a faulty relief valve or pressure that’s too high. Water from fittings or valves on top is often repairable. Water from the bottom or through the tank shell usually means the inner tank has failed — turn off the cold inlet and the gas or power, then call McDermott Plumbing on (08) 6187 3999 or text 0406 882 648 for replacement.
Relief valve: normal drip vs not
Mains-pressure storage systems have a temperature and pressure relief valve. As water heats and expands, a little discharge from the drain line is expected on many units. That’s not a flood — it’s a short drip or spit during the heat-up cycle.
A relief drain that runs constantly, hisses non-stop, or has turned the garden bed into a swamp is not normal. Causes include a relief valve that’s stuck or worn, inlet pressure above what the system should see (Australian Standards cap water pressure inside a home at 500 kPa — a pressure limiting valve may be missing or failed), or a thermostat that’s overheating the tank. All of those need a plumber, not a longer garden hose.
Leaking from the bottom — usually replace
When water is coming from the base of the tank, through the outer jacket, or pooling under the unit with no clear fitting above it, the inner tank has usually corroded through. That failure can’t be welded or patched in a domestic unit. The safe move is to isolate the cold water to the heater, turn off gas or power, and arrange a replacement.
Don’t keep running a tank that’s emptying itself into the laundry or garage. Apart from the water bill, you can damage flooring, plaster and electrics. Take photos for your records before clean-up if you’re claiming on insurance.
Leaks that are often repairable
- Inlet or outlet unions and valves on top of the tank
- Tempering valve drips
- Relief valve that needs replacing (when the tank itself is sound)
- Expansion control valve discharge that’s excessive because of pressure issues
- Circulated or solar loop fittings (system-dependent)
What to do before we arrive
- Work out where the water is coming from: relief drain pipe, top fittings, or the tank base.
- If it’s flooding from the base or a burst fitting, turn off the cold water to the unit (and the house stop tap if you can’t find the unit isolation).
- Turn off gas at the unit control or power at the hot water circuit — only if you can do it without standing in water.
- Mop or contain the water; keep power points dry.
- Text a clear photo to 0406 882 648 with your suburb and whether it’s gas, electric, solar or heat pump.
Repair, valve job, or new unit?
We’ll tell you on site. A relief valve and a pressure limiting valve can save a sound tank. A tank leaking from the shell needs replacing. Age matters: storage units commonly last around 8 to 12 years depending on water and maintenance, and many manufacturers recommend anode checks around the five-year mark.
For options when you’re replacing, see our hot water systems page and the 135 L gas storage units we supply. We don’t list prices here — you’ll get a clear scope before we start.
Common questions
- Is it normal for a hot water relief valve to drip?
- A small amount during heating is normal on many mains-pressure storage systems. A constant stream isn’t — that usually means a faulty valve or high pressure. Call a plumber.
- Why is my hot water system leaking from the bottom?
- Usually the inner tank has failed. That can’t be repaired. Isolate water and energy to the unit and call McDermott Plumbing on (08) 6187 3999 or text 0406 882 648 for a replacement.
- Can a leaking hot water system be repaired?
- Sometimes — fittings, valves and relief valves often can. A tank leaking through the shell generally means replace. We’ll say which you’re looking at before we start work.
- Will a leaking hot water system make my water bill spike?
- Yes, especially a relief valve that runs constantly or a tank emptying to waste. Fix it early. Visible appliance leaks aren’t treated as hidden leaks for Water Corporation’s leak allowance — see our leak detection page.
- Do you replace gas and electric hot water systems?
- Yes. Licensed plumbing and gas fitting for gas units, and electric storage and heat pump changeovers as part of our hot water work. Call (08) 6187 3999.
Related pages
Official sources
Last updated 2 October 2026. General information only. Every property is different, so call us to talk about yours.