Hot Water System Leaking: What the Leak Location Means

A leak from a hot water tank or its pipework is worth treating as urgent, because a storage system stays connected to the mains and keeps refilling as it loses water. A tank in a laundry cupboard, an upstairs room or against a wall can wet plaster, flooring and framing well before the drip looks dramatic.

The common exception is the drain pipe from the temperature and pressure relief valve. Rheem's troubleshooting guide says it is normal and desirable for that valve to let some water escape while the system heats, roughly 1/50 of the hot water you use, because water expands by about that much as it warms.

So the first job is not to judge how much water there is. It is to find where the water starts, and the sections below go through each location in turn. Queensland's Residential Tenancies Authority lists both a serious water service leak and a breakdown of the hot water service as emergency repairs, which is a fair guide to how seriously a real leak should be taken.

Isolating the system is the safe owner step, and it is the sequence Solahart, Thermann and Rheem print in their owner's guides.

Electric, solar with an electric booster, and heat pump systems: switch off the electrical supply at the system's isolating switch, then close the cold water isolation valve at the inlet to the water heater. Solahart's owner's guide gives that order, and Thermann's heat pump guide names the same two isolation points.

Gas storage systems: Rheem's owner's guide for its Stellar gas model says to shut down the gas control, close the gas isolation valve at the inlet to the gas control, then close the cold water isolation valve. If you can smell gas, do not try to relight the system: the same guide says to turn off the gas control and the gas isolation valve, leave the area and call a qualified service technician.

Stop at that point. Do not drain the tank, undo fittings or take covers off to see where the water is coming from. Solahart warns that its water heaters can deliver water hot enough to cause severe scalding, and the Queensland Building and Construction Commission (QBCC) says most plumbing work in Queensland must be done by a QBCC licensed plumber.

The temperature and pressure relief valve sits near the top of a storage tank with a drain pipe running from it. A drip from that pipe while the system is heating is the valve releasing expansion water, and Rheem's troubleshooting guide calls that normal. Solahart supplies an expansion control valve on the cold water line with each of its thermosiphon solar systems, and its owner's guide explains that this valve discharges instead of the relief valve because it has a lower pressure rating, so on a solar system the drip may come from a different pipe.

The line between normal and a fault is volume. Rheem says that if the valve discharges more than a bucket full of water in 24 hours, there may be another problem. Thermann's heat pump guide lists the possible causes of continuous discharge: excessive water supply pressure, a faulty relief valve or a faulty thermostat.

All three are jobs for a licensed plumber. Solahart warns that water from the relief valve drain line will be hot, so keep hands, pets and children clear of the outlet while you wait.

Water at the top of a tank often comes from the connections rather than the cylinder: the cold inlet and hot outlet fittings, the thread where the relief valve screws in, or a valve on the pipework close to the tank. A connection that has worked loose or a valve that has worn out is a part, and a part can be replaced on a sound tank.

Trace the wet patch upwards to where it starts. Water from a fitting can run down the outside of the tank and collect at the base, where it looks like the far more serious leak from the bottom.

A top leak becomes urgent when it sprays or runs steadily, or when water is reaching the electrical cover or a power point. In that case isolate the system as described above. Either way the fix is not an owner job: the QBCC classes maintaining, repairing or replacing a fitting as minor work, which needs no permit but must be performed by a QBCC licensee.

Water coming from the tank itself, from a seam, through the outer jacket, or pooling underneath with no fitting above it, is the one location that usually means the system is finished. Many storage tanks are a steel cylinder protected on the inside by a vitreous enamel lining and a sacrificial anode, which is how Rheem's Stellar guide describes its tank. Solahart's owner's guide explains that the anode slowly dissipates while protecting the cylinder, and that replacing the anode can extend the cylinder's life. Once that protection is gone and the steel corrodes through, there is no part left to swap.

Manufacturer warranties reflect that. In years 6 to 10 of Solahart's cover on a complete system, the remedy for a failed cylinder is a replacement cylinder, with the installation labour paid by the owner. RCM's position is the same. A cylinder that has corroded through is replaced, and we tell you that before any work starts.

Before calling it a cylinder failure, a plumber will check that the water is not coming from a fitting or component low on the tank. If it is the cylinder, turn the cold water off at the isolation valve and plan the replacement rather than waiting to see what happens.

A tank installed where a leak could damage the property, such as inside a laundry or upstairs, should sit in a safe tray: a shallow tray with its own drain pipe. Rheem's owner's guide for its Stellar gas model says that where damage to property can occur if the water heater leaks, it must be installed in a safe tray built to AS/NZS 3500.4.

Water in the tray, or running from the tray's drain pipe, is not a fault with the tray. It is telling you that something above it is leaking, so treat it as a pointer. Check whether the relief valve drain discharges near the tray, whether a fitting at the top is wet, or whether the water is coming from the tank body. The answer puts you back into one of the sections above.

A tray that keeps filling while the relief valve pipe stays dry is the pattern to worry about, because it points at the tank or its connections. People also call the relief valve drain the overflow pipe, so check which pipe is actually running before you describe it to a plumber.

On a roof-mounted solar system the tank sits on the roof with the collectors, so a leak can show up as a damp ceiling, a stain under the eaves or water running off the roof on a dry day rather than a puddle beside a tank. On a solar system the expansion control valve releases some water while the system heats, in place of the relief valve, so water from its drain pipe is often normal for the same reasons as on any storage tank.

Two things are different. First, do not go up to look. Solahart's owner's guide says not to climb onto a non-trafficable roof to reach the relief valve, and a wet roof only adds to the risk. Photos taken from the ground are enough to start with.

Second, colour. On closed circuit systems such as Solahart's, a heat transfer fluid circulates through the collectors and a jacket around the tank. Solahart says blue water at the taps, or blue fluid around the base of the tank or the collectors, indicates a leak of that fluid, and that the fluid is non-toxic and not hazardous to health. It is still a fault that needs inspecting.

A heat pump takes heat from the air passing over it, which cools that air enough for moisture to condense on the unit, much as it does on an air conditioner. Thermann's heat pump owner's guide says water may be expected to drain from the condensate drain line whenever the unit is operating, and that the amount depends on temperature and humidity. It is clean water from the air, not water from the tank.

Some high-efficiency gas storage units do the same. Rheem's owner's guide for its Stellar gas model says a plastic drain near the bottom of the unit will drip during the heating cycle and can discharge several litres of condensation a day, especially in cool conditions, and that this water is not from the mains supply.

What is not condensate is water from the tank body, from a fitting or from a pipe joint. If you are not sure which pipe is the condensate drain, a photo of the unit and its pipework usually settles it in one message.

Where the leak is settles most of the repair or replace question before anyone looks at the age of the system. Relief valve discharge within the normal range needs nothing. Heavy relief valve discharge, a leaking fitting or a worn valve is a part on a tank that may have years left, so it is usually a repair. A leak from the cylinder is a replacement, whatever the age.

The question people ask next is how long a tank lasts once it starts leaking from the body. There is no safe number. Corrosion that has reached the outside has already gone through the steel, and a leaking cylinder does not stay the same size. Plan the replacement now rather than running the tank until it fails completely.

If it is a part, age and parts availability still matter, and the repair or replace guide covers how those weigh up. If you rent, a breakdown of the hot water service is an emergency repair under Queensland tenancy rules, and the RTA says to contact the emergency repair contact on your tenancy agreement as soon as you know about it.

Where the water is coming from, in plain words: the relief valve pipe, a fitting at the top, the tank itself, the safe tray, the roof or the heat pump drain. Whether it is dripping, running or spraying, and whether you have already turned off the cold water and the power or gas.

The system type, and the brand and model from the data plate if you can read it without reaching over water or live connections. A rough idea of the system's age helps as well.

Three photos: the whole system from a step back, a close shot of where the water is, and the data plate. Between them a plumber can usually tell whether to bring a part or plan a replacement. RCM runs a 24 hour emergency call-out, seven days across the Sunshine Coast, and the call button on this page reaches it.