A plumber repairs pipes. A leak detection specialist finds the one that is hidden. When the plumber has checked everything visible and the damp or pressure loss continues, the next step is a non-invasive survey using thermal imaging, acoustic listening and tracer gas. The specialist marks the repair point, and your plumber then makes the repair.
The plumber came out, checked under the sink, looked at the bath waste, pulled the washing machine forward, ran the taps and went over every joint they could see. Nothing. The patch on the ceiling is still spreading, or the boiler gauge is still falling, and the last thing they said was that it must be under the floor somewhere. That is an honest answer, and it is not the end of the road. This guide explains why a good plumber cannot find a leak that is out of sight, what a leak detection specialist does that is different, how the two jobs fit together, and what you should have in your hand at the end.
Why a good plumber cannot see through a floor
A plumber is trained and equipped to repair. When a leak is visible, a weeping joint, a split flexi hose, a perished washer, they will find it in minutes and fix it in the same visit. The trouble starts when the leak is inside a wall, under a screed, in a floor void or in a buried supply pipe. There is nothing to look at. The only tools a plumber typically carries for that situation are experience and a willingness to lift something, and lifting something is a guess with a chisel.
Water also travels. A leak in a first-floor bathroom can run along a joist and show as a stain two metres from the source. A heating pipe leaking under a hallway can surface as damp at the base of a lounge wall. In a Cornish cottage with rubble stone walls and a suspended floor, water can go a surprising distance before it shows. A plumber opening the floor where the stain is will often find dry boards, close it up, and be no wiser. That is not poor work. It is the wrong tool for the job.
What a leak detection specialist does differently
Detection is diagnosis rather than repair. The visit starts with questions and system checks: what you have noticed, when it started, which circuit is losing water. Isolating the heating from the mains and watching how pressure behaves tells the engineer which system to search before any instrument comes out. Only then does the equipment follow, chosen to suit the pipe material, the floor build-up and the way the leak is behaving.
| Method | What it does | Where it is strongest |
|---|---|---|
| Thermal imaging | Maps surface temperature to show where hot or cold water is reaching a surface | Heating pipes in floors and walls, underfloor heating loops |
| Acoustic listening | Amplifies the sound of water escaping under pressure through a ground microphone | Mains and supply pipes, solid floors, buried pipes |
| Tracer gas | A safe hydrogen and nitrogen mix is put into a drained pipe and detected where it surfaces | Plastic pipes, deep floors, leaks too small to hear |
| Moisture mapping | Meters and readings across a wall or floor show the extent and direction of the wet area | Telling a leak from condensation or rising damp |
| Pressure and dye testing | Isolates sections and confirms which one is losing water | Bathrooms, waste pipes, pool and heating circuits |
The important word is cross checking. A professional survey does not mark a repair point on one reading. A warm patch on a thermal image is confirmed with a second method before anyone is told where to open the floor, because a thermal camera shows where the heat is arriving, not always where the hole is. Two methods agreeing is what turns a guess into a location. Our guide on what to expect from a leak detection survey walks through the visit in order.
How the two jobs fit together
The sequence is the same for almost every hidden leak, and keeping the order saves money at each step.
- Stop the water. If it is flowing, close the stopcock. If it is the heating, turn the boiler off if the pressure is collapsing, or leave it ticking over on low if the loss is slow, because a warm system is easier to survey.
- Find it precisely. The specialist locates the leak to a small area, usually a few hundred millimetres, and marks it on the floor or wall.
- Repair it. Your plumber opens that one spot and replaces the failed pipe or fitting. Because the location is known, the repair is small and quick.
- Make good. The floor, wall or ceiling that was opened is reinstated, which is often the part your insurer pays for.
Repair comes after finding, never instead of it. A plumber who opens three places to find one leak has made three holes to repair and a customer paying for all of them. A plumber who is handed a marked point makes one.
The handover back to your plumber
Some people worry that calling a specialist means starting again with a stranger. It does not. A detection specialist is not competing with your plumber for the repair. We locate, document and hand over. Most of the time the plumber who could not find the leak is exactly the right person to fix it once it is found, because they already know the house and the system. If you do not have a plumber, the report is written so that anyone competent can act on it.
The handover works best when the engineer and the plumber can talk directly, so tell us who your plumber is and we will describe the location and the pipe in terms they can use. The marked point on the floor, the photographs and the description of the fault together mean the repair visit can be booked with confidence about how long it will take.
What the report gives you
You leave the survey with a written report, and it does two jobs. For the plumber it records where the leak is, what pipe and material is involved, how deep it sits and how the location was confirmed. For your insurer it sets out the cause, the date, the methods used and the damage seen, with photographs and thermal images. Most buildings policies cover damage from an escape of water, and many include trace and access cover, which pays towards the cost of finding the leak and reinstating what was opened to reach it. The repair to the failed pipe itself is not normally covered. A report that shows a sudden, located failure is far stronger than a note saying the plumber could not find anything. Our guide to what trace and access insurance covers explains how that part of the claim works.
When it really is a simple fix
A hidden leak does not always need a specialist, and we would rather say so. If the water is visible, a plumber is the right call and the only call. If a dripping overflow, a running toilet or a loose bath panel explains the damp, fix that first and see if the problem goes. Where you have a water meter, close every tap and watch the dial for half an hour. If it does not move, the mains and supply pipes are probably sound and the search moves to the heating or a waste pipe. Our guide on a sound of running water in the walls covers the home checks in more detail.
Call a specialist when the plumber has checked everything visible and the loss continues, when the damp keeps returning after it has been dried, when the boiler needs topping up with no leak in sight, when the meter turns with everything off, or when the alternative is lifting a tiled or slate floor on a guess. In a Cornish house with an original stone floor, a survey is almost always cheaper than the second wrong hole.
A water leak detection survey is the next step in that situation. We provide leak detection across Cornwall, from Bude to Penzance, and we hand each located leak straight back to a plumber for the repair.
Frequently asked questions
What is the difference between a leak detection specialist and a plumber?
A plumber repairs pipes and fittings and finds leaks that are visible. A leak detection specialist locates hidden leaks using thermal imaging, acoustic equipment, tracer gas and moisture mapping, then marks the point and writes a report. The specialist finds, the plumber fixes. They are separate jobs, usually done by different people.
Does a leak detection specialist also do the repair?
Generally no. The survey ends with a marked repair point and a report, and the repair is carried out by your own plumber or one you choose. Because the location is known to a small area, the repair is usually a short job with one opening rather than several.
Can a plumber find a leak under the floor?
Sometimes, by lifting boards where the damp shows, but water travels before it surfaces and the first hole is often dry. Without thermal, acoustic or tracer gas equipment the search is a guess. For a solid or tiled floor a non-invasive survey is the safer route.
Will insurance pay for leak detection if the plumber could not find the leak?
Many buildings policies include trace and access cover, which contributes to the cost of locating a hidden leak and reinstating what was opened. Check your own policy and its limit. The repair to the failed pipe itself is not normally covered, and the report from the survey supports the claim.
What should I do while I wait for the survey?
Keep the water off if it is flowing, keep the heating on low if the loss is slow, and write down what you have noticed with dates and photographs. Note any pressure readings. Do not add leak sealer to a heating system, because it hides the evidence and makes the leak harder to trace.
Find it, then fix it
If your plumber has checked everything in sight and the leak is still running, we can locate it without opening floors on a guess. You get a marked repair point for the plumber and an insurance-ready report.
