EXPERT ADVICE
Leakage in water tank: What to do
Updated 08/26
By: Wendy Reynolds
Reviewed: Alex Peters
A leaking water tank rarely stays a small problem for long. Left alone, it can push up your water bills, damage ceilings and flooring, and eventually mean replacing the whole tank rather than a single part.
Here's how to spot it early, what causes it, and what to do next.
The early warning signs of a leaking water tank
Why the location of the leak matters for the fix
What to do in the first few minutes after spotting it
Whether it's a repair job or a replacement job
How much a water tank repair typically costs
How to stop it happening again
Signs of a leaking water tank
If you're not sure whether your tank is actually leaking, look out for:
Damp patches and water stains around the base of the tank, or on the ceiling below it
Dripping or gurgling noises coming from the tank itself
Falling water pressure, which often points to an unresolved leak
Mould or mildew, caused by the damp environment a leak creates
Rising water bills, without an obvious explanation
If you have a cold water storage tank in the loft, check it every few months even if nothing seems wrong. Freezing temperatures can crack fittings, and a slow leak can go unnoticed for weeks in an area you rarely visit.
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Why is my water tank leaking?
Where the leak is coming from tells you a lot about what's causing it, and what kind of repair you're looking at.
Leaking from the base
Usually a loose drain valve, incorrect pressure, or a worn temperature-pressure relief valve.
Leaking near the expansion tank
This often means the expansion tank itself needs replacing, though sometimes it's just a loose pipe fitting that needs tightening.
Leaking from the top
Typically caused by a loose cold water inlet valve or a corroded anode rod.
Leaking from inside the tank
This is harder to pin down, and usually caused by sediment build-up, excess pressure, or a corroded anode rod.
Overflowing or dripping from the overflow pipe
This is often a float valve that isn't shutting off properly, letting the tank overfill.
What to do if your water tank is leaking
Once you've noticed the signs, act quickly - the longer a leak runs, the more damage it can cause.
Find the source - dry the area and inspect the outside of the tank closely before any repair work begins
Turn off the power supply - switch off at the circuit breaker for electric tanks, or turn the gas shut-off valve to 'off' for gas-powered ones
Turn off the water supply - stop the leak getting worse straight away
Attempt a temporary fix if it's minor - tightening a loose valve or sealing a small external leak can sometimes buy you time
Call a plumber - a professional will find the exact cause and carry out a permanent repair, rather than a stopgap
Depending on the cause, you might also want to read up on water leak detection or how to fix a leaking overflow pipe before booking a plumber.
Can you seal a leaking water tank yourself?
It's possible to seal a small leak yourself if you have the right tools and the correct sealant for your tank's material - plastic, steel, and concrete tanks all need different products.
That said, sealing is usually a temporary fix rather than a permanent solution. If the leak keeps coming back, or if it's coming from a valve or corroded component rather than a hairline crack, you're better off getting a plumber to look at it properly.
Cold water storage tanks in the UK are subject to water quality regulations, since standing water can be a breeding ground for bacteria like Legionella if the tank isn't properly maintained.
A professional inspection isn't just about the leak - it's a chance to check the tank is safe.
What happens if you ignore a leaking water tank?
Even a small, slow leak is worth dealing with promptly. Left unaddressed, a leaking water tank can lead to:
Flooding in the room where the tank is installed
Ceiling damage, and in severe cases, ceiling collapse
Scalding risk, if a malfunctioning tank causes water temperature to rise unexpectedly
Fire hazard, from an overheating electric water tank
Gas leaks, if the tank is gas-powered and the fault relates to its gas components
Water tank leakage repair costs
Repair costs depend on which parts need replacing and how long the job takes. As a guide, hot water tank repairs average around £300, with plumbers typically charging £60 an hour, plus a call-out fee of around £150 if you need an emergency visit.
If the tank can't be repaired and needs replacing entirely, our unvented hot water cylinder cost guide has a full breakdown of installation costs, and our water leak detection cost guide covers what to expect if you need help finding the source of a hidden leak first.
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Checklist: dealing with a leaking water tank
Water tank leak checklist
FAQs
Very - even a slow drip can cause structural damage, mould, and rising bills over time, and some causes (like a corroded relief valve) can worsen quickly.
It's best to turn off the water supply and get it looked at first, especially if the cause isn't confirmed, since continuing to use the system can make the leak worse.
Dry the area completely, then check where water reappears first - if it's around a pipe connection rather than the tank body, it may be a pipework or fitting issue rather than the tank itself.
Many policies cover the resulting damage (like a ruined ceiling), but check your specific policy, as gradual leaks are sometimes excluded if they weren't reported promptly.
Most tanks last 10-15 years, though this varies with material, water quality, and maintenance - persistent leaks are often a sign the tank is approaching the end of its life.
It can be, particularly with electric or gas-powered tanks, where a fault can create a fire or gas safety risk alongside the water damage.
Yes - a leak can cause a noticeable drop in pressure, since water is escaping before it reaches your taps.
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