Tracer gas is a mixture of tracer gases introduced into empty pipes to locate leaks without breaking walls or floors. It works like this: the installation is emptied, pressurised with the gas, and the gas escapes through the break. A handheld detector picks up that gas at the surface and points to the area where the concentration is highest, which is directly above the leak. It is especially useful in plastic pipes, in installations with low pressure and in deep runs where the geophone does not pick up the sound well.
How tracer gas works
Tracer gas is a mixture of tracer gases. It is introduced with a pressurisation unit fitted with a pressure regulator after the installation has been emptied. Its composition, the working pressure and the safety measures are set by the technician according to the product and the applicable regulations.
The process is as follows:
- Emptying the installation: The section is isolated and drained through the low drain points; if water remains trapped, the technician expels it with compressed air. This is an important step, because the gas has to fill the pipe and trapped water prevents it.
- Controlled pressurisation: The tracer gas pressure regulator is connected to the isolated pipe. It is pressurised slowly, monitoring the pressure on a gauge. The pressure is kept low and controlled, and the technician adjusts it according to the type of pipe.
- Surface tracing: The technician walks the route of the installation at the surface carrying a portable electronic detector. Where there is a leak, the gas escapes into the atmosphere and the detector picks it up.
- Locating the point: The detector emits an audible and visual signal when it detects the gas. The technician refines the location by moving the detector until the peak concentration is found.
Why emptying and pressurising are required
Emptying the installation is necessary because the gas needs to fill the entire pipe to reach the leak. If pockets of water remain, the gas does not reach every point or advances very slowly. Pressurisation helps the gas reach the break, even if it is small.
The pressure is regulated below the safe limit of the installation and adjusted to the pipe material, with more care in old or fragile pipes.
When it is the right technique
Tracer gas is the right solution in these cases:
- Plastic pipes (polyethylene, PEX, multilayer): With plastic the geophone usually performs worse, because the material dampens the vibrations. Tracer gas does not depend on sound.
- Installations with low pressure: If the meter is shut off, the stopcock is closed or the network barely pressurises, the geophone picks up no noise. Tracer gas still works because it is simply injected into the pipe.
- Deep buried pipes: when depth or the ground dampens the sound, the geophone loses effectiveness and gas can be an alternative.
- Very small leaks: they may be silent for the geophone; gas can help locate them, although the result depends on the case.
- Water cut off in the home: without mains pressure the geophone usually does not work; tracer gas can be an alternative.
- Fire protection networks (PCI): In fire protection networks buried or complex systems, tracer gas can be useful for locating leaks in buried networks, depending on the case.
Limits of tracer gas
It has important restrictions:
- Requires access to the pipe: The section where the leak is suspected must be isolatable. In some complex installations with many branches, this requires closing several valves.
- Pipes with trapped water: If the installation cannot be fully drained (badly laid pipes, natural water pockets), the gas does not reach those points.
- Very long runs without access: In very long service connections without an intermediate access point, the gas can lose pressure and dilute into the atmosphere before filling the whole route.
- Old or fragile pipes: pressurising an installation in poor condition requires great care so as not to damage it; in some cases it is better to choose another method.
How the gas is billed
The quote should state how the gas is billed, and whether it is charged separately. A serious quote can break down the cost of the location work (technician, detector, travel) and the cost of the gas used. It is advisable to ask that the quote states a maximum for the gas. To understand better what determines leak detection prices, see our full guide on location costs.
The amount of gas required depends on:
- The volume of the pipe (diameter and length of the section to be inspected)
- The pressure applied
- The search time (if the leak is not found quickly, more gas is needed)
In practice, consumption depends on the complexity of the installation. That is why it is advisable for the quote to set a maximum and for the invoice to reflect the actual consumption.
What the technical report includes
After the location work it is advisable to request a written report. A useful report usually includes:
- Location: the leak point or points, referenced on a plan or sketch and with photographs.
- Technical description: what the pipe is and, if known, its material, diameter and approximate depth.
- Method used: which tests were carried out and on which sections.
- Repair recommendation: whether the case allows a repair without works (for example, resin rehabilitation) or whether the section has to be opened and replaced.
If you need a written report, check before hiring that the quote includes it and what its content will be.
When to call a professional
If you suspect a leak in a plastic pipe, your water is cut off, or the geophone has not given clear results, tracer gas is the next step. It is not a procedure to carry out yourself: it requires specialised equipment, knowledge of safe pressures and a calibrated detector.
Request a quote that breaks down the location work and the gas. Do the meter test beforehand (close all taps and check whether it moves): this confirms there is a real leak before you invest in location work.
For more context on other techniques, see our comparison of detection methods and the guide on how the geophone works. You can contact us for detection with tracer gas.
