The most common signs of a hidden water leak are damp patches or stains on walls, ceilings or floors, a musty smell, mould appearing in unusual places, a water meter that moves when nothing’s running, an unexplained rise in water bills, and a boiler that keeps losing pressure. Any one of these is worth investigating before it causes more damage.
A simple meter test will tell you whether water is escaping from the mains supply. For leaks in heating pipework, falling boiler pressure is usually the giveaway. If you can’t find the source, a plumber can trace it without pulling up more than necessary.
Common signs of a hidden leak
- Stains or tide marks on ceilings, especially below bathrooms or radiators
- Damp or soft patches in walls or floors
- Bubbling or peeling paint and wallpaper
- Warped flooring or lifting tiles
- A musty smell that won’t go away
- Mould in places that aren’t normally damp
- The sound of running water when everything is off
- A higher water bill without a change in use
- A water meter that moves when no water is being used
- Boiler pressure dropping repeatedly
Mains water leak or heating leak?
It helps to know which system is leaking, because they show up differently.
| Mains water supply | Central heating system | |
| Main clue | Meter moving, higher bills | Boiler pressure dropping |
| Where it leaks | Supply pipes, toilets, taps, showers | Radiators, valves, heating pipes, boiler |
| Water appearance | Clear | Often discoloured (black or brown) |
| Effect | Wasted water, damp | Pressure loss, boiler lockouts, corrosion |
How to check for a leak yourself
Water meter test
- Turn off all taps and water-using appliances
- Make sure no one uses water during the test
- Note the meter reading, or photograph the dials
- Wait at least 30 minutes, ideally longer
- Check the reading again
If it has moved, water is escaping somewhere between the meter and your taps. Leaks outside the property boundary are usually the water company’s responsibility; leaks on your side are usually yours.
Toilet check
A toilet constantly trickling into the pan is one of the most common, and most overlooked, leaks. Put a few drops of food colouring in the cistern and don’t flush. If colour appears in the pan within 15 to 20 minutes, the flush valve or fill valve is letting water through.
Heating system check
On a combi or system boiler, note the pressure on the gauge when the heating is cold. If it drops noticeably over a few days without you bleeding radiators, water is escaping from the heating system. See our guide on common central heating problems for more.
When to call a professional
Call a plumber or heating engineer if:
- The meter test shows a leak but you can’t see where
- A ceiling is bulging or sagging (turn off the water and stay out from under it)
- Water is near electrical fittings (turn off the electricity at the consumer unit if it’s safe)
- The boiler keeps losing pressure
- You find a leak under a floor or behind a wall
Leak detection methods can include pressure testing, thermal imaging and acoustic equipment, depending on the leak and the tools the engineer has.
Know where your stopcock is
The internal stopcock turns off the mains water supply to your home. It’s often under the kitchen sink, in a downstairs toilet or where the supply enters the house. Find it now and check it turns, so you can act quickly if a leak appears. Older stopcocks can seize, so if yours won’t turn, get it replaced.
Leaks in Surrey homes
Around Woking, Guildford and Camberley, many homes have had extensions and loft conversions added over the years, with new pipework joined to older runs. Those joints, and pipes running through loft spaces and under floors, are common spots for slow leaks to go unnoticed.
Frequently asked questions
Does home insurance cover hidden leaks?
Many policies cover damage caused by escape of water, and some include trace and access cover to find the leak. Check your policy wording, as cover varies.
Can a small leak cause serious damage?
Yes. A slow drip under a floor or behind a wall can rot timbers, damage plaster and encourage mould over months before it’s noticed.
Why does my boiler pressure drop if I can’t see a leak?
The leak may be hidden under floors or behind walls, or it could be the pressure relief valve discharging outside. An engineer can check both.
Think you’ve got a hidden leak?
Give us a call on 07557 373 042 or drop us a message and we’ll come and help track it down.
