A small drip while heating is the valve doing its job
The valve on the side or top of your storage tank is the pressure and temperature relief valve, the PTR. When your system heats water, the water expands and pressure rises. The PTR bleeds off that excess through the copper drain line so the tank never sees dangerous pressure. A cup to a litre a day, mostly while the system is actively heating, is normal operation, not a defect. If you have never noticed it before, it is usually because you have never stood next to the tank mid-heating cycle.
A constant stream means the valve or something upstream has failed
Water running steadily from the drain line at all hours is a different story. Either the valve seat has worn or scaled up and will no longer close, or the pressure coming into the valve is genuinely too high and the valve is doing exactly what it should. Both need a plumber. The common causes we find are a worn PTR valve, mains pressure above what the system is rated for, a failed expansion control valve where one is fitted, and a thermostat fault that is overheating the water. The fix is quoted on inspection because it depends entirely on which of those it is.
What your relief valve is telling you
| What you see | Most likely meaning | What to do |
|---|---|---|
| Occasional drip while heating | Normal thermal expansion | Nothing, this is correct operation |
| Steady drip or stream all day | Worn PTR valve or excess pressure | Book a plumber this week |
| Gushing or spurting hot water | Valve relieving a real fault | Turn off power or gas and water, call same day |
| Never drips, ever, even under test | Valve may be seized shut | Book a test, a seized valve is the dangerous one |
Never cap, plug or squeeze off a dripping relief valve
This is the one hard rule on this page. A dripping PTR valve is annoying. A capped one turns your tank into a pressure vessel with no relief path. Storage water heaters have burst when relief valves were defeated, which is why the valve and its unobstructed drain line are mandatory under AS/NZS 3500.4 and every manufacturer's installation instructions. If the drip is bothering you, the answer is to fix the cause, never to block the outlet.
Test the valve every six months, replace it about every 5 years
Manufacturers put a test schedule on the tank for a reason. Gently raising the easing lever every six months lets a burst of water flush the seat and confirms the valve moves freely. Most manufacturers recommend replacing the PTR valve around every 5 years, and on the Gold Coast we would not stretch that, because our water and coastal conditions are not kind to brass valve seats. In our experience the tanks that arrive at a burst or flooded end had valves that were never tested once. Valve replacement is a quick licensed job and we quote it on inspection, usually bundled with a general check of the anode, tempering valve and connections while we are there.
A dripping valve can also be your early warning of tank end-of-life
A PTR valve that starts weeping constantly on a tank past 8 to 12 years old is often the first symptom in a chain that ends with a leaking tank. Sediment, corrosion and pressure faults tend to travel together. If your tank is in that age range, it is worth pricing a replacement alongside the valve repair so you can make the call with real numbers. Electric storage replacements run $1,300 to $2,400 installed and gas storage $1,800 to $3,200 installed on the Gold Coast as of 2026.
Not sure which drip you have? Send us a photo or call Hills Plumbing & Gas on 0472 657 042 and describe what you see. We are QBCC licensed (licence 15243081), we give a fixed price before work starts, and we quote an honest ETA on the call. Details at our hot water systems page.
Sources: AS/NZS 3500.4 (heated water services); manufacturer installation and maintenance requirements for PTR valves; Queensland Plumbing and Drainage Act 2018.