Tracer Gas Leak Detection in London
Tracer gas leak detection works by introducing a hydrogen-nitrogen gas mixture — typically 95% nitrogen and 5% hydrogen — into isolated pipework under controlled low pressure. Because hydrogen is the smallest molecule in existence, it diffuses through fractures, failed joints, and pinhole leaks in the pipe wall, then rises through surrounding materials — soil, concrete screed, timber subfloor — to the surface above. A calibrated electronic gas detector is then swept systematically over the area to identify where the hydrogen is escaping, allowing your engineer to pinpoint the precise failure without lifting floors or excavating.
What Is Tracer Gas Detection?
Tracer gas is the method of choice when a temperature differential cannot be relied upon — which is precisely the condition that limits thermal imaging. It performs at its best on cold water supply pipes, buried garden feeds, and any pipework encased in insulation or surrounded by dense screed. Our engineers use tracer gas routinely for mains water leak detection, where cold feed pipes running beneath floors or through external walls carry no thermal signature even when actively leaking. It is also our preferred technique for underfloor heating leak detection in cases where the heating system has been off long enough for the screed to return to ambient temperature, making thermal cameras ineffective. The method penetrates ceramic tiles, hardwood boards, polished concrete, and carpeted surfaces with equal reliability, and works at depths of up to two metres — making it one of the most versatile tools in non-invasive leak detection.
Our engineers carry calibrated hydrogen detector units sensitive to concentrations as low as 1 part per million, along with specialist pressure gauges and isolation couplings for pipe connection. The tracer gas we use — a 95% nitrogen, 5% hydrogen blend — is non-toxic, non-flammable, and approved for use in occupied residential and commercial properties. Every survey is followed by a written report documenting test pressures, gas readings, and the confirmed leak location, formatted for submission to insurers and loss adjusters.
How Tracer Gas Detection Works
System Isolation and Pressure Test
Before any gas is introduced, your engineer isolates the suspect pipework by closing off the water supply and connecting specialist end caps or couplings to the pipe. A pressure gauge is fitted, and the system is pressurised with dry air or nitrogen to confirm that a pressure loss is occurring. This initial test establishes both that a leak is present and how significant it is — ensuring the pipe is correctly sealed before the tracer gas is introduced.
Introducing the Tracer Gas
Once the pipework is confirmed isolated and sealed, the hydrogen-nitrogen tracer gas mixture is introduced under controlled, low pressure through the coupling points. The gas — 5% hydrogen and 95% nitrogen — fills the entire pipe run and begins to escape wherever there is a fracture, joint failure, or pinhole. Hydrogen molecules, being exceptionally small, pass readily through concrete, screed, soil, and insulation, rising naturally toward the surface at the point directly above the leak.
Surface Scanning and Detection
Your engineer uses a handheld electronic gas detector to sweep methodically over every surface above the pipe route — floor coverings, wall faces, tiled areas, and insulated sections. The detector is calibrated to identify hydrogen concentrations as low as 1 part per million. As it passes over the escape point, readings escalate sharply. The engineer narrows the search progressively, grid by grid, until the leak is confirmed to within a few centimetres and marked clearly on the surface above.
Written Survey Report
Once the leak is confirmed and marked, your engineer prepares a detailed written survey report on the day. This document records the pipe tested, the test pressure applied, the gas concentration readings observed during the scan, and the confirmed leak location referenced to a floor or wall plan. The report is structured to meet insurer and loss adjuster requirements, and can be used directly to support a trace and access claim or a water damage restoration claim.
Tracer Gas Detection Situations We Handle
Cold water mains pipe under concrete floor slab
Underfloor pipe with no visible surface dampness
Buried garden supply pipe losing pressure steadily
Concealed pipe behind tiled bathroom or kitchen wall
Central heating pipe beneath insulated screed floor
Communal riser pipe shared between multiple flats
Post-renovation leak with no temperature differential
Insurance trace and access claim requiring evidence
Insulated or lagged pipe showing no heat signature
Trusted Across London
Absolutely quality service and what plumbers should exemplify. Turned up when they said, was kind, answered all my questions and wasn't being dodgy with anything. Skilful and efficient! Would highly recommend.
The technician arrived on time, was polite, and explained the process clearly before starting. They used advanced, non-invasive equipment to locate the leak quickly without causing any unnecessary damage to my property.
Really impressed with the service. They responded quickly and were able to accurately detect the leak without causing unnecessary damage. Professional, efficient, and clearly experienced — would highly recommend to anyone dealing with a hidden leak.
Wayne and his colleague came and within an hour found the leak deep underneath my cellar and came up with a perfect plan which made the pipe redundant and re-routed it the following morning. An excellent option if you're having a problem with a leak you cannot find.
Called Wayne Monday and he was round Tuesday evening — came out of hours to help me out. Very professional, punctual and great with communication. Fair priced too. Will definitely recommend and use again.
Contacted them and they were at the property within an hour. Honest, well priced and gave a detailed report that will likely save me hundreds of pounds. Will definitely recommend and if necessary will use again.
Wonderful efficient service — came out the same day, nothing was too much trouble. Engineers were professional and polite, explained the problem and persevered until the blockage was cleared. Would highly recommend this company.
The staff were so professional and friendly. The technician was nice and informative — he advised me the leak was outside and wrote me a report which I sent to Thames Water. In a few days they sent a repair team and found the leak. Clear Flow are great at what they do.
I received a letter from Thames Water about high water usage. Wayne arrived on time, was so professional, guided me through what he was doing and advised me of the next steps. He also wrote me a report to send to the water board. 100% recommend.
Deploying Tracer Gas Detection Across Greater London
Because structural anomalies dissipate as water migrates along joists and substrate, timing matters. Clear Flow engineers carry calibrated thermal imaging equipment and operate across all 32 London boroughs on a 24/7 basis — available for emergency callouts as well as planned surveys.
Coverage extends into Surrey and Kent, making this service available to residential and commercial clients throughout the wider South East. Whether tracking an active underfloor heating loss in a Central London apartment block or mapping damp ingress in an outer-borough extension, the same non-invasive approach applies across every deployment.
Coverage Areas
- Central & Inner London 24/7 emergency response
- Outer London Boroughs Same-day availability
- Surrey & North Kent Planned surveys & urgent callouts
FAQs About Tracer Gas Detection
What is tracer gas leak detection?
Tracer gas leak detection is a non-invasive technique for locating hidden leaks in buried or concealed pipework. A safe mixture of 95% nitrogen and 5% hydrogen is introduced into the isolated pipe under low pressure. Hydrogen — the smallest molecule in existence — diffuses through any fracture or joint failure in the pipe and rises through surrounding materials to the surface. A calibrated electronic detector is then swept over the area to identify where the gas is escaping, pinpointing the leak location precisely without drilling or lifting floors.
How accurate is tracer gas leak detection?
Tracer gas detection is one of the most accurate non-destructive leak location methods available. In most conditions it can pinpoint a leak to within a few centimetres on the surface directly above the pipe, even through 200mm of concrete screed or compacted soil. Our detector units are calibrated to identify hydrogen concentrations as low as 1 part per million. Accuracy can be slightly reduced in very porous or loose ground, where the gas may disperse across a wider area before surfacing — in which case we use a secondary cross-check scan to confirm the exact point.
How long does a tracer gas survey take?
A typical tracer gas survey takes between two and four hours for a single pipe run in a residential property, depending on the length of pipework and the complexity of site access. Longer runs — such as communal risers in blocks of flats or buried mains supply pipes across a garden — may require additional time. In the majority of cases, however, we are able to confirm the leak location and produce a written survey report on the same day as the visit.
Will my insurance cover the cost of a tracer gas survey?
Most home insurance and buildings insurance policies that include trace and access cover will meet the cost of a tracer gas survey where it is the most appropriate detection method. Our written survey report — which details the test pressures applied, the gas concentration readings, and the confirmed leak location — is accepted by the majority of UK insurers and loss adjusters. We are experienced in liaising directly with insurers on your behalf, and our reports are formatted to support trace and access and water damage restoration claims.
When would you use thermal imaging instead of tracer gas?
We use thermal imaging when a clear temperature differential exists between the leaking water and the surrounding structure — typically on active hot water or central heating systems, or where the affected pipe has been running continuously and the surrounding fabric has absorbed enough warmth to create a visible thermal anomaly. Thermal cameras are also faster to deploy across large areas, making them a good first-pass tool. Where no temperature difference exists — cold water mains, post-insulation pipework, or systems that have been shut off — tracer gas is the more reliable choice.
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Same-day and emergency appointments available across London and the South East. Most leaks found and fixed in a single visit.