Leak Under the Floorboards
- How urgent
- Caution
- Who fixes it
- A plumber
What's happening?
A pipe or joint under floorboards leaks quietly for weeks. By the time the boards soften, the joists may be wet, so catch it on early signs: a musty smell, a damp patch that appears and dries, a floor that feels cold, the sound of dripping, an unexplained rise in the bill or a water meter that turns with nothing on. Pipework sits under floors because it runs to radiators and taps, and any joint can fail. WaterSafe describes the meter test for a hidden leak. The Water Fittings Regulations say joints should not be concealed, which is why an access panel over a joint matters.
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What usually causes it?
- A failed compression or soldered joint on a pipe under the floor
- A pinhole in a copper pipe from corrosion
- A pipe damaged by a nail or screw through the floorboards
- A joint worked loose by pipe movement or an old repair
- A leak from an appliance connection or a bath or basin waste above
- A leak in a heating pipe rather than a supply pipe, which shows differently
- A slow leak on the supply pipe under a solid floor, which rises into the room
Is it dangerous?
Medium. Water under a floor wets joists and can reach sockets and cables running beneath. If water reaches a socket, light fitting or the consumer unit, do not touch it, switch off the supply at the consumer unit only if you can reach it without standing in water, and use the electrical emergency page. Do not lift boards over live cables.
Can I fix it myself?
Do the meter test as WaterSafe describes. Turn off every tap and appliance, note the meter reading, and wait a few hours without using water. If it rises, there is a leak. Check the stop tap by shutting it: if the meter stops, the leak is in your pipework after the stop tap. Look for the nearest sign, a damp patch or a cold spot on the floor, and lift one board to look, if you can do so safely. Shut the water off at the stop tap if you cannot trace it. Keep the readings and photos for the insurer.
When should you call a plumber?
Call a plumber when the meter confirms a leak, when you cannot find it, when boards are wet or soft, when water has reached electrics, or when the leak is under a fitted floor. A leak detection plumber uses listening and thermal tools. Tell your insurer as soon as you can.
What will the plumber actually do?
- Isolate the supply and run a pressure or meter test to confirm a leak in your pipework
- Pinpoint the leak with acoustic or thermal tools, with minimal lifting of boards
- Repair or replace the joint or pipe and fit an access point over any joint
- Dry out and check readings, with moisture levels recorded for the insurer
- Test the system under pressure and recheck the meter
Who fixes this
- Leak detection
- Leak repair
What it usually costs
- Leaking Pipe Repair Cost
- £100–£500 for an emergency burst pipe
Questions people ask
How do I know if I have a leak under the floorboards?
How do I find a water leak under the floor?
Does home insurance cover a leak under the floor?
Is a leak under the floorboards dangerous?
Sources & References
Before you book, read what to check before a plumber starts.
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