Hot water cylinder leaking: what to do next

Deal with the immediate risk first

Keep people away from a cupboard containing steam, unusually hot discharge or water around electrical connections. If normal heating controls can be reached safely from a dry location, switch off the heat source and seek urgent professional assistance. Do not reach past leaking pipes or touch wet switches to do so.

For escaping water, only use a clearly identified water isolation control if it is safe and you already know its purpose. Otherwise describe the situation when requesting help. Do not dismantle the system, force an unfamiliar valve or assume an isolated supply means that stored hot water is no longer hazardous.

A connection leak and a leaking vessel are different

Water can track down the cylinder jacket from a connection above, so the place where a puddle forms may not be the point of failure. Insulation and surrounding pipework can obscure the route. An engineer needs to establish the origin without simply treating the lowest visible wet patch.

A serviceable connection or attached component may be repairable. Damage to the storage vessel raises a different replacement question. The condition of surrounding components and the availability of suitable parts also matter. Avoid buying a replacement cylinder before the source has been confirmed unless there is already a documented diagnosis.

Understand visible discharge without interfering with it

On an unvented system, a tundish is a visible break in the discharge arrangement, often shaped like a small open funnel. Water passing through it can signal that the safety arrangement needs investigation. It is not the same as a hole in the cylinder vessel.

Do not cap the discharge pipe, wedge a valve closed or attempt to stop the flow by altering safety controls. Record whether the discharge is continuous or appears during heating, from a safe distance. The professional needs to establish the cause and assess the system rather than merely suppress the visible symptom.

Vented and unvented systems require different assessment

A vented cylinder normally has a storage cistern and an open vent; an unvented cylinder is supplied from the mains and uses pressure and temperature safety arrangements. A household description such as “water tank” does not establish which one is installed.

Photograph the label and the overall layout if you can do so without entering a hazardous area. Do not remove insulation, covers or panels to find a serial number. If the installation is in a loft or cramped cupboard, let the attending professional inspect it with suitable access rather than climbing around a wet system yourself.

Useful details for the enquiry

Tell us when the leak first appeared, whether it is increasing and whether the cylinder is still being heated. Describe any visible water route without touching it to test its temperature. Previous repairs and service records can help establish whether this is a new problem or a recurring symptom.

If water has reached the floor below, mention that separately. Keep away from bulging ceilings and affected electrical fittings. In a flat, alert the managing agent and any affected neighbour through the appropriate building contact, because access and damage control may involve more than one property.

• Postcode, cylinder make and a safe photograph of its label.
• A wider photograph showing where water appears, if safe.
• Whether leakage occurs constantly or around the heating cycle.
• Access arrangements and the person authorised to approve work.
• Any visible damage outside the cupboard or affected room.

How repair and replacement should be compared

The diagnosis should distinguish the failed item from consequential damage and explain what the proposed repair covers. Ask whether the surrounding installation has been checked and whether further work may be needed once the area is accessible. A quick stop to a leak is not always the same as completing the necessary repair.

If the vessel needs replacing, discuss capacity, heating source, available space and removal access. A like-for-like model may be appropriate, but the existing layout still needs assessment. Unvented work requires relevant competence, suitable safety arrangements and an appropriate building-control process; general plumbing experience alone is not sufficient evidence for every task.

Can the system stay in use while you wait?

There is no reliable blanket answer from a photograph. The decision depends on what is leaking, how much water is escaping, whether temperatures are abnormal and whether electrical equipment is involved. Do not continue operating a system that is steaming, dangerously discharging or wetting electrical connections.

Ask for instructions specific to the identified installation and situation. Never restart it merely because the visible drip has stopped: an intermittent fault may depend on the heating cycle. If a professional has isolated or labelled equipment unsafe, follow that instruction until the issue is resolved.

Arrange cylinder help in London

Loyal Plumbers handles cylinder assessment and replacement across London and inside the M25. We operate 24/7 with 10 active vans. Use the enquiry form with the visible symptoms and access details so the next step can be matched to urgency, rather than assuming every leak requires a planned replacement survey.

Keep the findings and repair records after the visit. If replacement is necessary, retain the commissioning and maintenance information alongside the equipment details. Follow the specific manufacturer’s maintenance requirements; guidance for one cylinder design is not a universal procedure for all stored-water systems.

Start with written details in the enquiry form. If photographs would help, the team can request them by email after your initial enquiry; the form does not accept image uploads. Only take photographs where access is safe.