Hot water cylinder leaking: what should you do?

Protect people before trying to protect the cupboard

A leaking cylinder can release hot water into a confined space containing electrical equipment. Keep children, pets and other occupants away, especially where water has spread beyond the cupboard. Do not reach around the cylinder or touch wet surfaces to find the source. A leak that looks modest from the doorway may have reached concealed connections, flooring or the area beneath the appliance.

If there is water near electrical equipment, WorkSafe advises that affected components need an electrician's safety check. Turn power off at the mains only if that can be done safely, without crossing water or touching wet equipment. Otherwise keep clear and seek urgent help. Do not remove the element cover, try a tripped breaker or restore power because the floor appears to have dried.

Follow an orderly response without dismantling anything

The sequence below is a way to organise a response, not a requirement to operate unfamiliar controls. Isolation valves can be awkward to identify, and a switch near the cupboard may not serve the equipment you expect. If you are uncertain, leave the controls alone and explain that to the plumber. Nobody should have to enter a wet or cramped space to complete a checklist.

For an active leak, say that water is escaping when you request emergency plumbing assistance. Describe whether the flow is continuing and whether electrical equipment may be affected. If there is immediate danger to people, contact emergency services. If you smell gas at any point, leave immediately and call the gas supplier or emergency services from a safe remote place rather than continuing the water leak checks.

1. Keep people away from the wet area and look for electrical or gas hazards from a safe position.
2. Arrange urgent professional help if water is flowing, spreading or approaching electrical equipment.
3. Switch off electricity only at a clearly identified control that can be reached safely from a dry position.
4. Close a clearly identified water isolation valve only if it is safely accessible and you understand which supply it controls.
5. Photograph visible water and surrounding damage without touching equipment or removing covers.
6. Tell the plumber what you observed and which supplies, if any, you have isolated.
7. Leave affected electrical equipment off until an electrician has confirmed it is safe to use.

Water beside a cylinder does not locate the failure

Water can travel along pipework or the outside of equipment before reaching the floor. A visible puddle may come from a connection above the cylinder, a valve, an adjacent pipe or the cylinder body. The point where water collects is therefore not necessarily the point where it escapes. Tell the plumber where you first noticed it and whether you could see an actual drip from a safe position.

Avoid tightening joints as an experiment. Movement can disturb connected plumbing, and a hot or pressurised fitting is not suitable for casual investigation. Do not pull back insulation or remove panels to follow a wet trail. Hot water cylinder repairs should begin with identifying the source and assessing the surrounding installation, rather than assuming that every puddle means a replacement cylinder is required.

Relief discharge needs a different kind of assessment

A discharge pipe is part of the system's safety arrangements, not an unwanted opening to seal. Manufacturer instructions explain that expansion during heating can produce discharge in some installations. Continuous or unusual discharge still needs assessment because the cause may involve controls, pressure or another fault. Without confirming which pipe you are looking at, it is unsafe to label every drip either normal or a failed cylinder.

Never cap, block or redirect a relief or vent outlet to stop visible water. Do not lift a valve lever while investigating an active leak unless a qualified professional has specifically assessed the situation and instructed you. Water discharged from the system may be hot. Note whether the water appears at an outside outlet, a gully trap or beside the cylinder, and pass that observation to the plumber.

Check for wider leakage only after urgent hazards are controlled

If the source remains unclear and there is no immediate hazard, the guide on how to check for a water leak explains how meter observations can help identify unexplained use. A meter test can indicate that water is being used somewhere, but it does not prove which pipe or appliance is responsible. Do not leave an active cylinder leak running just to complete a test or gather a longer record.

Watercare's leak guidance includes checking for cylinder relief valve discharge, dripping taps and damp outdoor areas. If there are wet patches away from the cylinder, unexplained running water or continuing usage after the apparent fault is addressed, leak detection may help locate a separate problem. Tell the plumber about previous water bills or damp patches, while keeping the immediate cylinder leak as the priority.

Repair and replacement depend on what has actually failed

A faulty external connection or valve may call for a different response from a leaking storage vessel. Ask the plumber to explain the identified source, the proposed repair and any uncertainty about the cylinder's condition. Age can inform the discussion, but it should not substitute for diagnosis. Photographs and a written description are useful when deciding whether to repair the current installation or plan a replacement.

If replacement is recommended, discuss pressure compatibility, household demand, access and any associated valve or pipework changes. Ask what is included in making the installation safe and operational, and whether electrical or gas work needs separate coordination. Do not assume a new cylinder can be selected solely by matching the old unit's outside dimensions. The installation requirements and the intended use both matter.

When to call a licensed plumber to assess cylinder leakage

Drying the visible area does not establish that wiring or concealed components are safe. An electrician should check electrical equipment affected by water before it is used again. A licensed plumber should confirm the plumbing repair and operating arrangements. If gas equipment is involved, use an appropriately licensed gasfitter for the relevant work. Check current practising licences through the Plumbers, Gasfitters and Drainlayers Board rather than relying only on a business name.

Where work changes hot water delivery, temperature protection also needs attention. MBIE states that new personal hygiene fixtures installed on or after 2 November 2024 generally have a maximum delivery temperature of 50°C when using the G12/AS1 compliance pathway. The change is not retrospective. Stored water should remain at at least 60°C to limit legionella risk, with delivery temperature controlled separately. Do not make thermostat adjustments yourself to compensate for a leak or an uncomfortable shower.