How to find a leak hidden under the floor
Check the steps below first — if you're not confident, get it fixed safely today.
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Most likely cause & what to check
The first evidence is usually: unexplained high water bills, damp patches on ceilings below bathrooms or kitchens, lifting vinyl or warping floorboards, or the smell of damp.
Confirm there is a leak by turning off all water-using appliances and checking the water meter. Take a reading, wait 30 minutes without using any water, and take another reading. If the numbers have changed, water is escaping somewhere.
Isolate the supply: turn off the hot water at the boiler or cylinder, then take the meter reading again. If the numbers stop moving, the leak is in the hot water circuit. If they still move, it's in the cold mains supply.
Listen: on ground floors above bare earth or concrete, you can sometimes hear a hiss from a leaking pressurised pipe. Use a listening stick (or just your ear against a screwdriver handle pressed to the floor) near the wet area.
A moisture meter (£15–£40 from a DIY shop) can detect elevated moisture through floorboards or plaster without needing to lift them. Sweep it across the floor to identify the hotspot.
Thermal imaging: plumbers and leak detection specialists use thermal cameras to find warm spots from hot water leaks. This is non-invasive and can save significant damage from unnecessary lifting of floors.
If the leak is in a screeded floor or under concrete, specialist leak detection is essential before you start digging — thermal imaging, acoustic leak detection, or tracer gas testing are all used by professionals.
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🛠 Tools & materials you may need
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