What Is in the Leak Detection Visit, Method by Method

What the visit covers in one paragraph

The visit is for one job: finding where water is escaping at a single domestic property in London and recording it. The price pays for locating the leak with every method it needs, and the written report, in one visit to a single domestic property in London. No VAT is charged.

What matters to a buyer is less the list than the rule behind it. No method on the list is billed on its own. The engineer does not price a thermal survey, then a tracer gas run, then an endoscope check as separate lines. They are tools in the same visit, used in the order the leak calls for, and moving from one to the next does not alter what you pay. The pricing page shows the figure beside what is quoted separately.

The sections below go through the methods one at a time. For each, you get what it detects, when it is brought out, what it cannot tell you, and the plain statement that it is part of the price. After the methods come the written report and the things that sit outside the visit.

Acoustic listening

Water escaping from a pipe under pressure makes a sound, and the sound travels along the pipe and through the structure around it. Acoustic listening uses sensitive microphones and amplifiers to pick up that sound at accessible points, such as stop taps, radiator valves and the floor or wall surface, and compares the signal along the run to find where it is strongest. It is usually the first method brought out for a leak on a pressurised supply pipe.

It cannot tell you much when the pipe is plastic, because plastic carries sound poorly, or when the leak is a slow weep that makes almost no noise. Background noise from traffic, a neighbour's plumbing or a running appliance also gets in the way. A good engineer tells you when listening has told them what it can and moves to something else, and that move is not billed. Acoustic listening is part of the price. No VAT is charged.

Thermal imaging

A thermal camera shows surface temperature differences. A hot water pipe leaking into a floor warms the surface above it, a cold supply leak cools it, and a wet patch in a wall usually sits at a different temperature from the dry wall around it. The camera is therefore a way of seeing where water or a pipe run is, without opening anything. It is also how a leak inside a radiator circuit or an underfloor loop can be followed across a room.

It does not show the water itself. It shows temperature, and temperature can be misleading: a cold external wall, a draught, sunlight on a window and a recently run bath all alter an image. For that reason a thermal image on its own is a pointer and not a conclusion, and the engineer checks it against another method before saying where the leak is. Thermal imaging is part of the price. No VAT is charged.

Tracer gas

Tracer gas is a harmless, very light gas mixture that is introduced into a pipe run which has been emptied of water. The gas escapes at the point of the leak and rises through the structure, and a sensitive detector passed over the floor or wall picks it up where it is strongest. It is the method for a leak that makes no sound and leaves no temperature difference, which describes many slow leaks in screed, behind tiles and inside walls.

It needs a run of pipe that can be isolated and emptied, so it takes longer to set up than listening or imaging, and it is used when the earlier methods have narrowed things down but not settled them. It does not work well in a space with a strong draught, and it only tests the circuit the gas was put into. On many other sites, tracer gas is a named extra and the cylinder is a line on the bill. Here it is not: the gas and the cylinder are part of the price. No VAT is charged.

The practical consequence is that the decision to use tracer gas is made on the evidence and not on the bill. A separate guide on this site goes into tracer gas in detail.

Moisture meters and moisture mapping

A moisture meter measures how wet a surface or the material just under it is. Mapping means taking readings across a wall, floor or ceiling on a grid and recording them, so that the wet area has a shape and a centre. Water travels, and the lowest or most visible damp is rarely directly below the leak. A map of readings shows the direction of travel and points back towards the source.

Moisture mapping is also how you separate a current leak from an old one. Damp that has stopped growing and is drying looks different on a map from damp that is still being fed. It cannot find a pipe, though, and it cannot tell leaking water from condensation or rising damp without the other methods alongside it. Moisture mapping is part of the price. No VAT is charged.

Endoscope inspection

An endoscope is a small camera on a flexible lead that goes through a small hole or an existing gap, such as under a bath, behind a service panel or through an inspection point, and shows what is inside the void. It answers the question that readings only suggest: is there a joint dripping, a corroded pipe or a wet insulation run behind this panel?

Its limit is access. It can only see where the lead can reach, and a pipe buried in solid screed or behind plasterboard with no gap is out of its range. It also shows a leak at a moment in time and may miss one that only runs when a particular tap or appliance is in use. Endoscope inspection is part of the price. If a small hole is needed to get the lead in, the engineer says so first, and any making good beyond that is quoted separately. No VAT is charged.

Pressure testing and dye testing

Pressure testing isolates a circuit, brings it up to pressure and watches whether it holds. A circuit that loses pressure has a leak somewhere on it, and one that holds does not, which lets the engineer rule whole sections of pipework in or out before looking for the position. It is how a heating circuit, a hot water run or a supply branch is cleared or implicated quickly.

Dye testing puts a coloured, harmless dye into water that you cannot otherwise follow, such as a bath, a shower tray, a basin overflow or a cistern, and watches where it appears. It is the straightforward answer to the question of whether water seeping out below a fitting is coming from that fitting. Neither method gives you a position inside a structure by itself. Pressure testing says which circuit and dye testing says which source. Both are part of the price. No VAT is charged.

Trace and access, and what it does and does not mean here

In the trade, trace and access has two halves: tracing the leak to its source, and then opening enough of the structure to reach it. In this price, the tracing half is included. Following the leak with the methods above until the source is identified is the work of the visit.

The opening half is not. Cutting into a floor, wall or ceiling to reach the pipe, and making good afterwards, is building work. It is quoted separately in writing before anything is opened, and the making good is done by a partner team and priced per job. Making good, such as walls, ceilings and decorating, is quoted per job by a partner team. This is the single point where buyers misread "every method" most often, so it is worth stating plainly: tracing is in the price, and opening up and making good are not. No VAT is charged.

The opening walls or floors page explains what an opening usually involves, so that a separate quote is not a surprise when it arrives.

The written report

Every visit ends with a written report that says what was found, where it was found and how it was confirmed, with the readings that support it. It is part of the price and is not a second invoice. If an insurer, landlord or managing agent asks for evidence of the leak, the report is what you send them. Whether your policy responds to anything is decided by your insurer, and the policy wording decides; the report does not change that, it gives them something solid to decide from.

The report records findings and does not name a person at fault. If the source proves to be a neighbour's pipe or a communal riser, it says what was measured and where. The report page shows what a report contains. No VAT is charged.

What sits outside the visit

A leak detection visit ends when the leak has been found and written up. What happens next is a separate decision with a separate quote. The repair itself, opening up and making good, commercial or multi-unit buildings, and underground work that needs a different set-up are quoted separately, in writing, before any work starts.

In practice that means four things. The repair itself: A small fix, such as tightening a fitting or changing a small part, can be done on the spot once the leak is found, and is quoted first, and for a longer repair the leak is stopped first, and the repair is quoted in writing after that. The opening of a structure and its making good. Commercial premises and larger multi-unit buildings, which are scoped and agreed in writing before attending. And underground work that needs a different set-up. Nothing in that list is added without a written quote you have accepted. No VAT is charged.

The what the price does not cover page lists these with the reasoning, and the pricing page shows them beside the detection price in one table.

• The repair itself, quoted in writing, with parts and materials agreed first.
• Opening up and making good, quoted per job.
• Commercial and larger multi-unit buildings.
• Underground work that needs a different set-up.

How the methods fit together on a real visit

On a typical visit the methods are used as a sequence of narrowing questions. Pressure testing asks which circuit is losing water. Listening and thermal imaging ask roughly where along it. Moisture mapping asks which way the water is travelling. Tracer gas or the endoscope asks the exact position. Dye testing asks whether a fitting is the source of what you can see. Not every visit uses every method: many leaks are settled by two or three, and the others stay in the case.

A decision on the next method is made on what the last one showed, and not on what it costs. That is the whole difference between this arrangement and a metered one. The how it works page takes the same sequence and walks through the decisions in order.