How to Find a Water Leak Under the Floor (Before Ripping It Up)

A leak under the floor is the most disruptive kind to imagine and, handled properly, one of the least disruptive to fix. The trick is knowing what the floor is telling you before anyone reaches for a crowbar.

The warning signs, in order of reliability

No single symptom proves an under-floor leak, but the combination usually does:

• Your boiler keeps losing pressure. A sealed heating system that needs topping up weekly is losing water somewhere — and buried heating pipes are a prime suspect.
• A warm patch on the floor. If one section of tile or timber is noticeably warmer than the rest and you don't have underfloor heating, a hot-water pipe below may be leaking.
• The water meter moves with everything off. Turn off every tap and appliance, note the meter reading, wait an hour, check again. Movement means a live leak on your side of the meter.
• Swollen or lifting flooring. Timber cups and laminate lifts at the edges long before you feel moisture.
• Musty smell or mould at skirting level. Damp trapped under a floor migrates to the edges of a room first.
• A water bill that jumped without explanation. Compare like-for-like quarters; a 20–30% unexplained rise deserves investigation.

The DIY checks worth doing

1. The meter test

This is the single most useful check a homeowner can run. Close the internal stop tap. If the meter keeps moving, the leak sits between the meter and your house — an underground supply pipe issue. If it stops, reopen the stop tap, turn everything inside off, and watch again: movement now points to internal plumbing.

2. The pressure gauge test

For heating leaks: repressurise your boiler to 1.5 bar with the system cold, then leave the heating off overnight. A drop by morning means the sealed system is leaking — in the boiler, a radiator, or the pipework between them.

3. The listening test

At night, with the house silent, put your ear to the floor near suspect areas. A pressurised leak often produces a faint, continuous hiss. Crude, but it has pointed many of our customers to the right room before we arrived.

What professionals do differently

Professional leak detection is a process of elimination with the right instruments at each step:

1. Isolate and pressure-test each circuit — mains, heating, hot water — to establish which system is losing water and roughly how fast.
2. Thermal imaging — with the heating running, an infrared camera shows the buried pipe runs through the floor surface. A leak appears as a bloom that spreads beyond the pipe line.
3. Acoustic detection — ground microphones follow the hiss of escaping water through screed and concrete to its loudest point.
4. Tracer gas — for the stubborn cases: the pipe is drained and charged with a safe hydrogen mix that rises through the floor at the exact failure point.

The outcome is a marked spot, typically accurate to centimetres. The floor is opened once, at the right place, and the pipe is repaired and retested.

What it costs to get wrong

The expensive version of this story is always the same: exploratory demolition. Lifting a floor room by room costs more than professional detection, and every unnecessary opening is a repair bill of its own. Water damage compounds too — a leak that soaks a joist for three extra months turns a plumbing job into a carpentry job.

If the checks above point to a leak under your floor, book a detection visit. We locate it without the crowbar, on a no find, no fee basis.