What Is Tracer Gas Leak Detection?

How does tracer gas leak detection actually work?

It works by introducing a traceable gas into a sealed pipe or damp structure, then following that gas back to its exit point with a hand-held detector. The mixture is usually 5% hydrogen and 95% nitrogen: safe, non-toxic, non-flammable at that ratio, and lighter than air. Hydrogen is the smallest molecule available, so it escapes through the tiniest cracks and joints that water alone might only seep from slowly. Once the gas rises to the surface through flooring, screed or plaster, the detector alarms at the precise spot, giving a clear location to investigate.

Why is it better than guessing where a leak is?

Because it pinpoints the source rather than the symptom, which stops you from opening up the wrong wall or floor. Water travels. A damp patch on a ceiling can originate metres away from where it appears, tracking along joists, pipes and membranes before it shows. Tracer gas cuts through that uncertainty by following the actual leak path.

• No unnecessary destruction of floors, tiling or plaster
• Works on pressurised pipes, heating systems and flat roofs
• Effective where acoustic or thermal methods struggle
• Suitable under concrete, screed and suspended floors
• Fast, with many leaks located in a single visit

When should tracer gas be used instead of other methods?

Use it when a leak is hidden, intermittent, or under a solid surface that other techniques cannot read reliably. A thorough investigation usually layers several techniques rather than depending on one. Thermal imaging maps temperature patterns, moisture meters confirm affected areas, and acoustic equipment listens for pressurised water. Tracer gas is brought in to confirm the exact point, especially on buried or non-pressurised pipework. You can read more about our full approach on our leak detection page.

What signs suggest you have a hidden leak?

The clearest signs are damp that keeps returning after redecoration, unexplained water bills, or a boiler that loses pressure without an obvious cause. Watch for the following:

• Damp patches on walls, ceilings or floors that spread or reappear
• Persistent musty smells in a room that never fully dries
• Warm patches on a floor above heating pipes
• Peeling paint, bubbling plaster or lifting tiles
• A water meter that ticks over when everything is switched off
• Mould returning in the same spot despite cleaning

What does the leak detection process involve?

The process is methodical and designed to confirm the source before any work begins.

1. We inspect the property and review the history of the damp or pressure loss.
2. We isolate the suspected pipe or system and prepare it for testing.
3. We introduce the hydrogen-nitrogen tracer gas under controlled pressure.
4. We sweep the area with a detector to locate exactly where the gas escapes.
5. We cross-check findings with moisture readings and, where useful, thermal imaging.
6. We document the confirmed leak location and its implications.

Where leak detection sits within a wider damp problem, a comprehensive damp and mould survey from Damp & Mould Solutions UK is a fixed £500. That fee delivers a full insurance-ready written report with a photographic evidence appendix, clear findings and prioritised recommendations, so you know precisely what is wrong and what to tackle first.

What affects the cost of fixing a leak once it is found?

The survey fee is fixed, but the cost of remedial work depends on factors that can only be judged once the leak is located. These include how accessible the pipe is, whether it sits under concrete or a suspended floor, the type of pipework involved, the extent of any water damage already caused, and whether reinstatement of flooring or decoration is needed. Pinpointing the leak first, rather than guessing, keeps that later work as contained as possible. We set out the findings in words in your report so any contractor can quote accurately.

Arrange your leak investigation with Damp & Mould Solutions UK

Damp & Mould Solutions UK carries out precise leak detection and comprehensive damp and mould surveys across London, including Kensington, Chelsea, Westminster, Camden, Islington, Hammersmith, Richmond and the surrounding boroughs. Call us on 020 3051 8478 or send photos via WhatsApp for an initial view of your problem, and we will advise on the right approach.

If you've got damp, mould, or a leak — you already know it needs sorting.

The longer it sits, the worse it gets. Most investigations are booked within 48 hours.