Hot water relief valve leaking or dripping: what it means

Every storage hot water system has a relief valve, and most people never notice it until they spot water dripping from a pipe near the tank or trickling out onto the ground outside. Before you panic or ignore it, it helps to know what that valve is doing and when a drip is telling you something is wrong.

What the relief valve actually does

The valve on the side or top of a storage tank is a PTR valve, short for pressure and temperature relief. It is a safety device, and it is compulsory on tanks in Australia. Its job is to let a little water escape if the pressure or temperature inside the tank climbs too high. Without it, a tank has no way to release that build-up. The small copper or plastic pipe running from the valve down towards the ground is the drain line, and any water the valve releases runs out of there.

Many systems also carry a second valve, the expansion control valve, fitted on the cold inlet. It does a similar job on the supply side and can drip for the same reasons.

A small drip while heating is normal

Here is the part that surprises people: a bit of dripping is meant to happen. When the burner or element kicks in and heats the water, the water expands. That extra volume has to go somewhere, so the relief valve opens briefly and lets a small amount out. You might see a cupful over a heating cycle, usually more noticeable in the afternoon or evening after a day of hot water use. In 40 years Terry has reassured plenty of homeowners that an occasional drip during heating is the valve doing exactly what it was designed to do.

When a leak means something is wrong

The drip stops being normal when it turns into a constant stream or a steady leak that never really stops. A few common causes:

• A worn or aged valve. The rubber seat inside a PTR valve hardens and fails over time, usually after five to ten years, and then it will not seal shut. It weeps constantly.
• Mains pressure too high. If your street pressure is above roughly 500 kPa, the valve is pushed open all the time. The fix is a pressure limiting valve on the mains, or an expansion control valve to give the expanding water somewhere to go.
• Grit or debris holding the valve open. Sometimes a bit of sediment lodges under the seat and stops it closing.

A relief valve that runs constantly is not just annoying. It wastes a surprising amount of hot water and money, and a valve that has seized shut is genuinely dangerous, so this is not something to leave for months.

What is safe to DIY and when to call Terry

There is one small maintenance job most people can safely do: gently lifting the little lever on top of the valve for a second to flush any grit, then letting it snap back. Do this once or twice a year and it can stop a valve sticking. Take care, because the water that comes out is scalding hot.

Beyond that, replacing a PTR valve, fitting an expansion control valve or adding a pressure limiting valve is licensed plumbing work. It involves draining the tank, matching the correct valve rating and testing it properly, and getting it wrong can leave a pressure vessel without a working safety valve. That is not a DIY job.

If your relief valve is running a constant stream, dripping heavily, or you have not tested it in years, Terry can check the pressure, work out whether it is the valve or your mains, and fix it with a fixed price quoted first. Give Terry a call on 0415 274 542.