Tracer Gas Leak Detection in London: The Rig, the Reading and the Cylinder Charge
Tracer gas leak detection puts a hydrogen and nitrogen mixture into an emptied pipe or sealed circuit, then follows it with a hand-held detector to where it escapes. It finds leaks under floors and behind walls without opening them first. Tracer work is £180 an hour plus £80 for each gas cylinder. No VAT is charged.
What the visit covers
- Isolating the suspected pipe run or heating circuit and filling it with the tracer mixture
- Sampling along the floor, skirting, walls and fittings with a hand-held detector
- Marking the strongest reading so any opening, if one is needed, is small
- A written report of what was found and where, with the readings recorded
Published prices
What it costs
- Fixed-price leak location package
- The package gives one fixed price, known before the visit, to locate a leak in one property using whichever methods the leak needs.
- £580Fixed price
Or by the hour
- Tracer gas leak detection
- Tracing a pipe run with tracer gas. The gas cylinder is charged once, on top of the hourly rate.
- £180an hour
Tracer gas work is charged £80 per gas cylinder on top of the hourly rate.
No VAT is charged
A fixed hourly rate that cannot rise on the day
No find, no fee applies when a live leak inside your own property cannot be located. No find, no fee in full
Order of work
Isolate and fill
The run under suspicion is shut off from the rest of the system and filled with the mixture from a cylinder through a regulator. Water is taken out first where the circuit allows, so the gas has room to move.
Sample the surface
A detector draws air through a thin tube, and a probe on a long handle puts the tube tip against fittings, skirting edges and floor joints. The operator moves slowly, because gas takes time to rise and drift.
Mark and compare
Readings are compared with a background reading taken elsewhere in the room. The highest point is marked, then checked from a second angle before anyone considers an opening.
Report the finding
The report records the circuit tested, the readings and the position. Where the gas and a visible fault agree, the case is closed. Where they do not, the report says so. See how tracer gas finds a leak for the full sequence.
What the rig looks like in use
The kit is a gas cylinder, a regulator with a gauge, a hose to the pipe or circuit under test, and a hand-held detector with a sampling tube. Nothing about it is large. It goes up stairs and into a boiler cupboard like any other toolbag, and what turns up at the door describes what is checked on arrival.
The mixture is usually 5% hydrogen in nitrogen, often sold as forming gas. Forming gas against helium compares sensitivity and cost. One industrial gas supplier describes the 5% blend as colourless, odourless, non-toxic and not flammable, and also as a suffocating gas that needs ventilation in confined spaces. That second point is why the room is aired and the cylinder is never left open.
The detector shows a number in parts per million. That number is only meaningful against a background reading taken in the same room that day. A real case is on record: on a heating manifold job the detector read 378 at the manifold and 34 at a nearby fitting, and a leaking flow meter was visible at the high point. Those figures belong to that instrument and that room.
The cylinder charge, stated before the visit
Tracer work is £180 an hour, and the gas used is charged at £80 for each cylinder on top. No VAT is charged. The rate is a fixed hourly rate that cannot rise on the day, so the hourly figure agreed beforehand is the one that applies.
Because hourly work does not have a total fixed in advance, the alternative that does is the £580 package for locating a leak for a leak in one property, with no VAT is charged, and tracer gas included by default. If tracer gas looks likely, compare the package with the hourly route and the cylinder charge before booking. The cost of tracer gas detection page works through both.
When tracer gas will not give an answer
A pipe that cannot be isolated, so the gas never reaches it, will not be tested. A sealed floor finish, a thick screed or a deep slab can hold the gas below the surface so the detector sees little. Wind from an open window can blow a reading away. A pipe that is leaking only under pressure, with a tiny weep that closes up when the pressure drops, can pass a gas test and still lose water.
On one visit in N10 a rig was set up over a concealed loss beside a thick concrete floor, and the record contains no reading. When tracer gas does not work lists the cases, and acoustic detection or a pressure test is then the next step.
If the leak cannot be located
No find, no fee applies when a live leak inside your own property cannot be located. A leak that belongs to a neighbour, a communal pipe or the water company main is a located leak and is charged. Ruling a leak out is also an answer, and is charged. The no find, no fee terms set out the boundary. If a claim is involved, the written report is the record an insurer assesses; cover depends on the policy and the insurer decides, as insurance-covered leak detection explains.
Sources and dates
Facts about the gas mixture were checked in October 2026 against the product page for a 95% nitrogen, 5% hydrogen mixture published by an industrial gas supplier (Woikoski, product page for Formier 5, read October 2026). Detector figures come from the job records behind this site and are not general thresholds.
Questions customers ask
Is the gas safe to use in a home?
Yes, with ventilation and care. The usual 5% hydrogen in nitrogen mixture is described by its supplier as non-toxic and not flammable. It can displace air in a small enclosed space, so the room is ventilated and the cylinder is shut when not in use.
How is tracer gas work charged?
Tracer work is £180 an hour, plus £80 for each gas cylinder. No VAT is charged.
Can I pay one price instead?
Yes, for a leak inside one property: the package is £580, and tracer gas is one of the methods it can use. No VAT is charged.
Will you have to open the floor?
Not before the leak is marked. The gas reading says where to look, and any opening afterwards is as small as the position allows. Opening and making good are separate from the detection.
What if the pipe passes the gas test?
A clean gas test removes that pipe from the list, and the survey moves to another method. It does not prove nothing is leaking, because a leak that only opens under pressure can pass.