A thermal camera detects temperature differences on surfaces, not water. When a leak causes a temperature change (especially with hot water), the camera can see it; with cold water at ambient temperature, usually not. That is why it is useful as a supporting technique, not as a definitive method: it complements the geophone, tracer gas or the pressure test. It is a specialised and limited technique.
What a thermal camera sees and what it does not
Infrared thermography displays the heat emitted by objects as colours: red/orange for warm areas, blue/green for cold ones. In leak detection it sees these cases:
- Active hot water pipes: The hot lines under the floor or embedded in walls are visible while hot water circulates. A leak interrupts that line or enlarges it.
- Underfloor heating with the system on: The circuit draws hot lines under the floor covering. A leak appears as a "blurred" area or a patch where a clear line should be.
- Evaporating moisture: Leaked water that evaporates consumes thermal energy and cools that area. The wet zone under the surface may look colder than its surroundings.
What it does NOT see:
- Cold water pipes or drains: water at a temperature close to ambient. The camera cannot tell the pipe apart from the floor around it.
- Very small leaks: the temperature change is so slight that it is confused with normal variations in the floor.
- Very deep pipes: heat dissipates with depth, reducing thermal contrast.
- The pipe itself, precisely: it shows where there is a thermal difference, not the exact location of the tube. A leak near the pipe may be interpreted as a leak in the pipe.
False positives: temperature changes that are not leaks
Thermography produces many false positives in domestic settings:
- Insulation differences: Areas where the slab has less thermal insulation, even without a leak, look colder or warmer than their surroundings.
- Hidden structure: A concrete beam embedded under the floor looks colder because concrete conducts heat better than earth.
- Entry of outside cold: North-facing walls or areas above unheated basements accumulate cold locally.
- Ventilation ducts: An air-conditioning or ventilation duct looks cold, as if it were a leak.
- Past moisture without a current leak: An area that was wet weeks ago still shows a different thermal reading even though the original leak has stopped.
That is why thermography never gives a diagnosis on its own. It is an indicator of "something thermally abnormal is here", not of "the leak is here".
When thermography is used as support
In hot water and heating circuits
If a leak is suspected in hot water pipes or underfloor heating, the system is switched on and thermal images are recorded. The hot circuit is clearly visible. If the leak is active (hot water is escaping), it visually interrupts the heat pattern or enlarges the thermal area. That indicates where to place the geophone or the tracer gas. See our full guide on leaks in heating to understand the symptoms and location methods.
To rule out moisture without a leak
A damp patch on a wall can have many origins: capillary rise, condensation, a past leak. Thermography can help, with limitations, to tell whether the moisture appears active or stagnant. It does not confirm a leak, but it helps guide the diagnosis. If there is moisture on walls, a thermographic inspection can be useful as a complement to other techniques.
To plan the search
In complex systems (underfloor heating with several circuits, heating with multiple branches), thermography traces the route of the pipes. That makes it possible to know where to trace with a geophone without walking blind.
Why it does not confirm a leak on its own
Many leaks have no clear thermal "symptom", or the symptom is ambiguous:
- Cold-water leaks: A break in the supply pipe or cold-water distribution (house inlet) often produces no measurable thermal change if the pipe is deep or poorly insulated.
- Slow leaks: A micro-leak accumulates water very slowly. There may be no detectable thermal change for days or weeks.
- Pipes in technical spaces: Under a floor slab, in shared building ducts, where air moves constantly, thermal changes dissipate quickly.
That is why, when a leak is suspected, the correct sequence is: (1) water meter test to confirm loss, (2) zoning and pressure test to narrow down the section, (3) geophone or tracer gas to locate, (4) thermography if necessary to confirm or rule out something specific. Not the other way round.
Summary: thermography as a support tool
Infrared thermography is useful but is never the complete method of detection. It is indicated for hot water and underfloor heating circuits as a complement to the geophone or tracer gas. On its own, it produces too many false positives to be reliable.
If you suspect a leak, the most reliable first check is the water meter: close all taps and see whether it moves. Once the leak is confirmed, choose the technique or combination of techniques according to the type of pipe and the situation. To understand how the geophone works, see its detailed guide. Also review the comparison of detection techniques to understand when a geophone, tracer gas or thermography is used.
