FLIR radiometric · Non-destructive · Insurance-ready reports
Thermal Imaging Leak Detection London
Pinpoint hot water, heating and hidden pipe leaks in walls, floors and ceilings — without opening the structure. FLIR E86 and E96 radiometric cameras, moisture-confirmation cross-check, loss-adjuster-format report.
Book a Thermal SurveyGet a Survey Quote
Thermal imaging — the second-pass method that finds what acoustic misses
Thermal imaging is the leak detection method for situations where the leak is real but acoustic listening cannot pinpoint it. Underfloor heating buried in screed under a hardwood floor — the pipe is inaccessible to a contact microphone. A hot-water leak inside a stud wall where the pipe route is unknown. A ceiling drip below a first-floor bathroom where traffic noise from a busy road masks the acoustic signature. In every one of these cases, thermal imaging works where acoustic cannot — because it reads the effect of the leak on the surface of the wall, floor or ceiling rather than the sound of the leak at the pipe itself.
The equipment matters more here than on almost any other detection method. A cheap non-radiometric thermal camera produces a colour picture — pretty, but useless for leak analysis because the pixel values are not calibrated temperature readings. A modern radiometric FLIR camera (the E86 we use for standard surveys, or the E96 for high-resolution riser and commercial work) records every pixel as a true calibrated surface temperature reading, saved as a FLIR .jpg with embedded metadata plus a companion .csv file of raw temperature data. A loss adjuster reviewing the report six weeks after the survey can open the file in FLIR Tools Pro and re-analyse any pixel — this is what makes a thermal survey report insurance-defensible.
The Noise Equivalent Temperature Difference (NETD) of our FLIR cameras is below 30 milliKelvin — the sensor detects a temperature difference as small as 0.03°C. That level of sensitivity is what allows the leak plume to be visible on the image even when the differential between the leaking water and the surrounding wall is only a few degrees. Combined with a controlled survey distance (30–80cm from the surface), a properly disciplined baseline capture before conditioning, and a moisture-meter cross-check at every pinpoint, we deliver a survey where a thermal hot-spot is a leak and not a chimney breast, a warm-air duct or a patch of sunlight.
Every thermal survey we run is delivered by a Water Regulations 1999 competent engineer (UK Certification Ltd certificate 136356 issued 8 September 2025, expiry 18 August 2030) with G3 unvented hot water certification (certificate 136359, same date range). Public liability £5,000,000 via SiriusPoint through Eaton Gate MGU, policy BE26ACTT000000018221, period 07/05/2026 to 06/05/2027. The full method-suite comparison — thermal versus acoustic, tracer gas, moisture mapping, CCTV — is on the main leak detection hub page.
The five-stage thermal survey — baseline to pinpoint
Every thermal survey we run follows the same disciplined sequence. Skipping the baseline stage is the single most common reason low-quality thermal surveys mistake structural hot-spots for leaks — and the reason customers end up with unnecessary opened walls.
Baseline thermal scan of the affected zone
Before the heating or hot water system is put into a specific state for the survey, the engineer captures a baseline radiometric image of the affected wall, floor or ceiling. This baseline records the ambient temperature distribution — cold spots from ventilation, warm spots from sunlight through windows, the thermal shadow of internal wall studs. Without a baseline, any hot-spot detected later can be misread as a leak when in fact it is just structural or environmental. The baseline is included in the written survey report.
System conditioning — hot circuit heated to differential
For a hot water or heating leak survey the circuit under suspicion is fully heated to at least 15°C above ambient. On a heating primaries survey the boiler is set to run at maximum flow temperature (typically 70–80°C) for 20 minutes before the imaging begins. On a hot water cylinder survey the immersion or boiler heats the cylinder to storage temperature (60°C or higher). The temperature differential between the leaking water and the surrounding structure is what makes the leak visible on the thermal image — a small differential means a small leak signature.
FLIR radiometric sweep at controlled distance
Using a FLIR E86 or E96 thermal camera (calibrated NETD below 30 mK, meaning the sensor can detect a temperature difference as small as 0.03°C), the engineer sweeps the affected area at a controlled distance of 30–80cm. Every image captured is radiometric — each pixel records both a visible thermal reading and the calculated surface temperature, saved as a FLIR .jpg with embedded metadata plus a companion .csv file. This means the loss adjuster reviewing the report can re-analyse any pixel weeks later, not just look at the pretty colour image.
Pinpoint by thermal signature — plume or shadow
A pressurised hot-water or heating leak produces a characteristic plume: a warm patch above the pipe run that follows the leak trajectory (up under gravity if the leak sprays, sideways if it wicks through structure). A cold-water leak on a heated circuit produces the inverse — a cold shadow along the pipe run where the leaking cold water cools the surrounding warm structure. The engineer identifies the pinpoint at the point where the plume or shadow is at its most extreme temperature, then confirms by capturing a second image at right angles.
Confirm with moisture mapping and mark on plan
A thermal hot-spot alone is not proof of a leak — sunlight, hot ductwork, chimney breasts and radiators all produce false positives. Every thermal pinpoint is cross-checked with a Protimeter capacitance moisture meter which reads the moisture content of the wall or floor at the identified point. Elevated moisture at the thermal hot-spot confirms the leak. Both readings are marked on the survey plan with x-y offsets from a fixed reference and included in the written report.
When thermal imaging is the right method
Thermal is the correct first-pass method wherever the pipework is inaccessible to a contact microphone, or where the leak effect is more visible on the wall/floor surface than in the pipe itself. Four common London scenarios:
Underfloor heating leak in a screed-covered pipe
Damp patch appearing on a downstairs floor with UFH. The pipe run is buried in screed under tile or hardwood, inaccessible to acoustic contact listening. FLIR thermal imaging with the UFH loop heated to 45°C flow shows the leak as a hot plume at the pinpoint, with the leaking water tracking sideways through the screed. Single tile lifted, keyhole repair, screed patched — no full floor rip-out.
Ceiling damp below a bathroom — hot pipe drop
Damp patch on a downstairs ceiling below a first-floor bathroom. Acoustic listening under the ceiling is inconclusive because the leak-noise is masked by traffic. Thermal imaging from below (after the shower has been run for 15 minutes) shows the hot pipe drop from the loft, with the leak signature at a specific soldered joint where the pipe passes through the floor plate.
Hidden hot-water pipe in a solid stud wall
Warm patch on the outside face of a stud wall between a kitchen and a hallway. Thermal imaging identifies the pipe route (which was not on the property survey drawings) and pinpoints a corroded compression joint on a 15mm hot flow at the point where the plume peaks. Access panel cut, joint remade.
Communal heating riser in a mansion block
Third-floor flat reporting cold radiators despite the block heating being on. Thermal imaging on the riser shaft between the plant room and the fourth floor identifies a leak at the two-storey height where the flow pipe is above the return. The leak has been reducing flow pressure in the upstream circuit. Freeholder-authorised repair with block still heated on emergency electric backup.
The FLIR kit — why radiometric matters for insurance
Radiometric imaging is the specification difference between a leak detection report a loss adjuster accepts and one they reject. Every image we capture is a calibrated FLIR .jpg — the loss adjuster can re-analyse any pixel weeks later in their own copy of FLIR Tools. The kit we deploy:
FLIR E86
Handheld radiometric thermal camera. 464×348 IR resolution, NETD <30 mK, 24° lens for standard survey plus a 42° wide-angle for large ceilings. Every image radiometric.
FLIR E96
High-resolution 640×480 IR sensor for large-format surveys — communal risers, plant rooms, warehouse and commercial buildings. Used where standard resolution cannot resolve the leak plume.
Protimeter Surveymaster BLD5365
Dual-mode moisture meter (pin and capacitance). Used to confirm elevated moisture at every thermal pinpoint — the confirmation that a warm patch is a leak, not a structural artefact.
Testo 872 (backup)
Secondary thermal camera carried on every survey as backup and for second-angle images. 320×240 resolution — used to cross-check FLIR readings in complex thermal environments.
Radiometric FLIR Tools Pro (report software)
Desktop software for post-survey pixel-by-pixel re-analysis. Every image in the survey report is re-analysable by the loss adjuster in their own copy of FLIR Tools.
When thermal imaging is not the right method
Thermal is a powerful method inside its operating envelope. Outside that envelope it produces unreliable results — and we tell customers upfront rather than deploy it and produce a false negative. Five common scenarios where thermal is not the right first-pass:
| Limiting factor | Effect on thermal survey |
|---|---|
| Solid stone floor with high thermal mass | Slower to show a hot plume — the stone absorbs heat before it reaches the surface. Longer conditioning time (30+ minutes) required, or supplement with acoustic. |
| Very small leak (below 5 ml/min) | Thermal signature may not develop enough differential from ambient. Combine with tracer gas or moisture mapping over a longer observation window. |
| Cold water leak on an unheated circuit | Cold water at 12°C leaking into a wall at 18°C produces a weak thermal shadow. Better suited to acoustic listening or tracer gas. |
| Recent heat source in the same area | A radiator, hot cupboard or sunlight-warmed wall produces false positives. The baseline scan (Stage 01) is critical to distinguish structural heat from leak heat. |
| Very high ambient (summer solar gain) | When the ambient wall temperature is above the leak-water temperature, the thermal contrast falls. Best survey time in these conditions is early morning before solar gain builds. |
Cost — thermal imaging leak detection surveys
Every thermal survey is quoted in writing before the engineer travels. Prices below are indicative; exact cost depends on property size and circuit accessibility. The no find, no fee guarantee applies on every scope.
| Survey scope | Price (inc. VAT) | Includes |
|---|---|---|
| Standard thermal survey (single wall or ceiling zone) | £300–£400 | Baseline scan, system conditioning, radiometric sweep, moisture cross-check, written report with FLIR jpg + CSV within 24 hours |
| Full-property thermal survey (multi-zone, single-family home) | £400–£550 | All heated zones, radiometric imaging, comparative moisture mapping, full written report |
| Underfloor heating leak survey (single zone) | £350–£450 | UFH loop conditioning, thermal sweep of the affected floor, pinpoint marked on plan, keyhole repair scope estimate |
| Communal riser thermal survey (mansion block, per riser) | £450–£650 | Multi-storey imaging with high-resolution E96 camera, freeholder-format report with GPS-style pinpoint |
| Insurance-triggered thermal survey (loss adjuster instruction) | £350–£500 | Same protocol, report formatted to loss-adjuster specification, phone briefing available |
| Second-opinion thermal survey (already surveyed elsewhere) | £350–£450 | Independent full-protocol survey. Signed-off finding regardless of previous survey outcome |
Real London thermal surveys
Three recent thermal imaging surveys, anonymised. Kit, method, pinpoint and outcome.
Chiswick town-house — underfloor heating leak in kitchen screed
Damp patch on the parquet floor of a ground-floor kitchen. UFH loop heated to 45°C for 25 minutes then imaged with FLIR E86 — leak plume identified 2.1m from the north wall along the second east–west loop. Single parquet plank lifted, screed opened over a 200×200mm patch, hairline crack on the PEX loop repaired with a push-fit coupling and re-screeded. Kitchen back in use within 48 hours. Total survey plus repair £820.
Islington conversion flat — ceiling drip below bathroom
Damp expanding across a lounge ceiling below the upstairs shower room. Acoustic under the ceiling picked up no clean signature (traffic noise on the road below). Thermal imaging after the shower was run for 15 minutes showed a hot plume from a soldered elbow on the shower waste feed inside the ceiling void, 1.8m from the party wall. Access hatch cut in a discreet corner, elbow re-soldered, hatch made good. Total £450.
Marylebone period building — communal riser flow-pipe leak
Upper floors of a five-storey mansion block reporting reduced heating flow and unexplained boiler top-up. FLIR E96 riser survey between the basement plant room and the fifth floor identified a hot plume behind plasterboard at the fourth-floor landing. Freeholder-authorised access hatch cut, pinhole leak on a 42mm horizontal flow pipe brazed and lagged. Block heating maintained throughout via the second riser. Full survey plus report £750 (freeholder cost), repair separately quoted.
Thermal imaging leak detection across every London borough
Same FLIR method and radiometric report format across all 32 London boroughs. Click a borough for a page tailored to local plumbing patterns.
Frequently asked questions about thermal imaging leak detection
How does thermal imaging leak detection actually work?
Will thermal imaging work on a cold-water leak?
Does the property need to be heated for the survey?
Can thermal imaging locate leaks under solid stone floors?
How is thermal imaging different from acoustic detection?
Are your thermal images accepted by insurance loss adjusters?
What certifications do your engineers hold?
Do you carry public liability insurance?
What if the thermal survey does not find the leak?
How long does a thermal survey take?
Related plumbing services
Leak detection — main hub
Full explanation of every detection method and when each applies.
Acoustic leak detection
The first-pass method for pressurised leaks — deployed alongside thermal on most surveys.
No find, no fee leak detection
Written guarantee terms and insurance workflow.
Hot water cylinder replacement
Cylinder leaks are a leading cause of ceiling damp on flats — thermal imaging often locates them.
Book a thermal imaging leak survey
Written no-find-no-fee quote before the engineer travels. Radiometric FLIR report within 24 hours.
Request a Survey Quote