A leaking water heater: where the water is coming from

If water is dripping from the safety valve, that is usually normal

Most electric and district-heating boilers have a safety valve on the cold water inlet, often with a small pipe or funnel underneath that leads to a drain or a bucket. As the water inside heats up it expands, and the valve lets a small amount escape so pressure does not build up in the tank. A few drops during or just after heating is normal operation, not a fault.

The problem is worth a closer look if the dripping is constant rather than occasional, or if it has clearly increased over the past weeks. A valve that never stops running usually means it has worn out or that mains pressure is too high for it, and either way it is cheap to replace and not something to ignore, since a stuck valve can eventually mean no pressure relief at all.

If water is coming from a fitting or pipe, that is usually repairable

Follow the water with your eyes and a dry cloth before assuming the worst. Wipe the pipework, the valve connections, and the fittings where pipes screw into the tank, then check a few minutes later to see where the moisture reappears first. A leak at a threaded joint, a compression fitting, or the flexible hose to the tank is usually just a loose connection or a worn washer.

This kind of leak is straightforward plumbing work: tightening a fitting, replacing a rubber seal, or swapping a corroded olive on a compression joint. It is exactly the sort of job our plumbing service handles, from 45 € per hour, and it is rarely worth leaving once you have located it, since a slow drip at a fitting has a habit of becoming a faster one.

If water is coming from the tank body itself, that is corrosion and cannot be repaired

If the water is seeping from the curved steel body of the tank rather than from any joint or valve, that is corrosion from the inside working its way out. This happens over years as the internal coating and the sacrificial anode wear down, particularly in older tanks that have not had the anode checked or replaced. Once water is visibly weeping through the metal, the tank wall has already been breached.

There is no patch, sealant, or weld that fixes this safely on a pressurised hot water tank, and anyone who tells you otherwise is setting you up for a repeat call in a few weeks, possibly with more water damage the second time. At this stage the only real options are living with a bucket until you replace the tank, or arranging the replacement itself, which is a job we can quote once we have seen the tank or a few photos of the nameplate and installation.

When to shut the water off straight away

A slow, occasional drip from the safety valve or a fitting you have already identified can usually wait until you have arranged help. A leak that is steady, growing, or coming from the tank body itself should not wait, because a full tank of failing steel can go from a weep to a split with little warning.

Shut off the cold water supply to the tank at the isolation valve on the inlet pipe, which is normally a small lever or wheel valve close to where the pipe enters the top of the unit. If you cannot find it or are not sure which valve controls the tank, shutting off the main stopcock for the flat or house is the safer default until someone can confirm the right one.

• Shut off immediately: steady leak from the tank body, water pooling faster than it can be mopped, a burst pipe rather than a leak
• Can usually wait a few hours: occasional drips from the safety valve, a fitting leak that is slow and has been marked or timed
• Always shut off if you are leaving the flat unattended, regardless of how minor the leak currently looks

What you can check yourself before calling for help

Before anyone comes out, a bit of your own checking saves time and often the call-out itself. Wipe every joint dry, place something under the tank to catch and show where drips land, and note whether the leak happens constantly, only during heating, or only when hot water is drawn off elsewhere in the flat.

A photo of the nameplate on the tank, showing the make, model, and litre capacity, is useful even if the fault turns out to be a corroded tank needing replacement rather than a repair. If you have a Soviet-era panel flat with the tank in a cramped bathroom cupboard, a photo also helps us judge access before arriving with the right fittings the first time.

Can you fix a leaking tank yourself

Tightening an obviously loose fitting with the correct spanner, without forcing it, is reasonable if you are comfortable doing it and the water is already shut off. Beyond that, we would not recommend it. Working on a pressurised tank that is still connected to mains water and, on an electric unit, to mains power, carries a real risk of scalding or electric shock if done blind.

If the fault turns out to be electrical rather than plumbing, such as a heating element housing that has started to seep, that work goes to a qualified electrician rather than being tackled as plumbing. For everything else, from a stuck safety valve to a full replacement, our plumbing service starts at 45 € per hour, and for the odd bracket, cupboard panel, or bit of carpentry needed to get at the tank, our general odd jobs service starts at 39 € per hour.